Merge branch 'fix_warnings_unused_function' into 'master'

ref:staging/dune-uggrid Added preprocessor if-conditions and commented out
some unused functions to avoid compiler warnings made by CI test
"gcc-7-14-sequential".

See merge request [!127]

  [!127]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/127

Deleted the function "CheckNodeContext" because it was not used in.
````
static INT CheckNodeContext (ELEMENT *theElement, NODE ** NodeContext)
{
  INT i, mark,nor,noc;

  mark = MARK(theElement);
  for (i=CORNERS_OF_ELEM(theElement); i<CORNERS_OF_ELEM(theElement)+EDGES_OF_ELEM(th       eElement); i++)
  {
    if (NODE_OF_RULE(theElement,mark,i-CORNERS_OF_ELEM(theElement))) nor = 1;
    else nor = 0;
    if(NodeContext[i]!=NULL) noc = 1;
    else noc = 0;
    if(nor!=noc)
      if (GetNodeContext(theElement,NodeContext)) REP_ERR_RETURN(1);
  }
  for (; i<CORNERS_OF_ELEM(theElement)+EDGES_OF_ELEM(theElement)+SIDES_OF_ELEM(theEl       ement); i++)
    if (NodeContext[i]!=NULL)
      if (GetNodeContext(theElement,NodeContext)) REP_ERR_RETURN(1);

  return (0);
}
````

Deleted the definition of "CheckLocalElementKeys" for the case
````
!(MGIO_DEBUG>0)
````
because all uses in this file are contained in a preprocessor if condtion ensuring
that
````
MGIO>0
````

The function was not needed.

Added a preprocessor if condition around the definition of
"Write_RefRules" because it is used in such an environment.
````
static INT Write_RefRules (MULTIGRID *theMG, INT *RefRuleOffset, INT MarkKey)
{
  ...
}
````

Furthermore there is a comment adressing the only use of "Write_RefRules".

````
/* TODO (HRR 971209): drop old call of Write_RefRules */
  #if EXTRACT_RULES
if (NEW_Write_RefRules(theMG,rr_rule_offsets,MarkKey,&rr_rules)) REP_ERR_RETURN(1)       ;
      #else
if (Write_RefRules(theMG,rr_rule_offsets,MarkKey)) REP_ERR_RETURN(1);
      #endif
````
But i am not sure whether "Write_RefRules" is still needed.

Added a preprocessor if conditon around the definition of "FillSonPaths"
because the only use in this file is contained in such an if condition.
````
 #ifdef __THREEDIM__
static void FillSonPaths (MGIO_RR_RULE *rule)
{

 ...

}
 #endif
````

````
        #ifdef __THREEDIM__
  /* 2D: not even in rm */
  /* son path */
  FillSonPaths(mr);
        #endif
````

I added a preprocessor if-condition to the definition of "RuleCompare"
because the only use in "gm/er.cc" is contained in such an environment in line 698

````
 #ifdef __DEBUG_ER__
static INT RuleCompare (int id, const URULE *ur, const ERULE *er)
{
  ...
}
 #endif
````

````
        #ifdef __DEBUG_ER__
  ...
  RuleCompare(ID(elem),ur,er);
  ...
        #endif
````

I added a preprocessor environment to contain the definiton of the
function: "CheckElementContextConsistency"

````
 #ifdef Debug
static void CheckElementContextConsistency( arguments )
{

 ...

}
 #endif
````
because the following use of the function is also contained in such an
environment.

Merge branch 'fix/gcc9-warnings' into 'master'

See merge request [!136]

  [!136]: Nonestaging/dune-uggrid/merge_requests/136

Merge branch 'fix-vector-leaf-index' into 'master'

ref:staging/dune-uggrid The 'skip' data member of the Vector class used to be
abused for the leaf index of the vector, if that vector corresponds to an
element facet in 3d. By accident, that 'skip' field got removed in a recent
commit. Let's put it back in, but rename it to 'leafIndex' now. All it is used
for nowadays is that leaf index.

See merge request [!141]

  [!141]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/141

The 'skip' data member of the Vector class used to be abused for
the leaf index of the vector, if that vector corresponds to an
element facet in 3d.  By accident, that 'skip' field got removed
in a recent commit.  Let's put it back in, but rename it to
'leafIndex' now.  All it is used for nowadays is that leaf index.

Merge branch 'master' into 'master'

ref:staging/dune-uggrid Removed vector::skip and the code that uses it. It
compiles and the few existing tests run without problems.

Fixes [#29]

See merge request [!139]

  [#29]: gitlab.dune-project.org/NoneNone/issues/29
  [!139]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/139


Closes #29

See Issue `#29`.
Removed `vector::skip` and the  code that uses it. It compiles and the
few existing tests run without problems.

Avoid GCC 9 warning

Merge branch 'issue/unused_macros_dim_max' into 'master'

ref:staging/dune-uggrid The macros DIM_MAX and DIM_OF_BND_MAX are not used
anywhere and the DIM_MAX macro conflicts with macros from other libraries. So
they are simply removed. The corresponding `#undef DIM_MAX` should be removed
from dune-grid.

See merge request [!135]

  [!135]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/135

Merge branch 'build-tetrahedron-refrules-into-library' into 'master'

ref:staging/dune-uggrid The TET_RULESET compile-time option could be used to
load tetrahedron refinement rules from RefRules.data, however this requires to
locate the file at run-time. This was too inconvenient.

Instead generate RefRules.cc from RefRules.data including the refinement rules
and use that.

See merge request [!134]

  [!134]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/134

The `TET_RULESET` compile-time option could be used to load
tetrahedron refinement rules from `RefRules.data`, however this
requires to locate the file at run-time.  This was too inconvenient.

Instead generate `RefRules.cc` from `RefRules.data` including the
refinement rules and use that.

Merge branch 'use-std-abs' into 'master'

See merge request [!133]

  [!133]: Nonestaging/dune-uggrid/merge_requests/133

Merge branch 'use-standard-deprecated-attribute' into 'master'

See merge request [!132]

  [!132]: Nonestaging/dune-uggrid/merge_requests/132

Merge branch 'cleanup-33' into 'master'

See merge request [!131]

  [!131]: Nonestaging/dune-uggrid/merge_requests/131

This addresses the following compiler warning from GCC 9:

    gm/ugm.cc:1247:12: warning: unused variable ‘f’ [-Wunused-variable]

This addresses the following warning from GCC 9:

    parallel/ddd/xfer/unpack.cc:410:11: warning:
    ‘curr’ may be used uninitialized in this function [-Wmaybe-uninitialized]

The variable is currently not used; just remove it as the include for
`DUNE_UNUSED` is sometimes missing.

Merge branch 'fix_warning_set_but_unused_nSendMsgs' into 'master'

ref:staging/dune-uggrid

    Added the attribute "DUNE_UNUSED" to the variable "nSendMsgs" to avoid the
    warning:"variable 'nSendMsgs' set but not used".

See merge request [!125]

  [!125]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/125

Merge branch 'change_function_structure_gm_rm' into 'master'

ref:staging/dune-uggrid Changed the structure of three functions in "gm/rm.cc"
that threw a warning.

Deleted the variable TBFR which is now unused in each of the functions. Moved
the declaration of variables to their initialization and added a new "switch
case" to avoid an if condition in each function.

See merge request [!128]

  [!128]: gitlab.dune-project.org/staging/dune-uggrid/merge_requests/128

Moved declarations of variables to their initialization and restricted
their scope.

Added a new case for "imin" to get rid of the if condition and deleted
the now unused variable "TBFR".

Merge branch 'ci-build-with-debug' into 'master'

See merge request [!129]

  [!129]: Nonestaging/dune-uggrid/merge_requests/129

Merge branch 'fix/remove-include-no-longer-around' into 'master'

See merge request [!130]

  [!130]: Nonestaging/dune-uggrid/merge_requests/130