Merge branch 'fix-warnings' into 'master'

See merge request [!277]

  [!277]: Nonecore/dune-istl/merge_requests/277

Merge branch 'feature/amg-memory-management' into 'master'

ref:core/dune-istl This branch is cleaning up the AMG memory management in
order to get rid of manual pointer juggling and thus improve maintainability.

See merge request [!274]

  [!274]: gitlab.dune-project.org/core/dune-istl/merge_requests/274

if on the initial AMG pre was called, it is currently it not necessary to
call pre on a copy of that AMG. This is a feature that is not required
by the Preconditioner interface and thus it nothing anybody can rely on.
We now don't copy the temporary data anymore.

Hierarchy and MatrixHierarchy now have separate headers to improve
readability.

like all other preconditioners we now use shared_ptr to be able to go
via the base class.

this is a first step to cleanup memory management in the AMG and it will
facilitate the construction of an AMG using a factory.

* we introduce a new constructor taking a shared_ptr<MemberType>
* all old constructors are deprecated
* we update the test and the AMG implementations to the shared_ptr and
  pass it to Hierarchy

Merge branch 'fix-copy-n-paste-bug' into 'master'

See merge request [!263]

  [!263]: Nonecore/dune-istl/merge_requests/263

Merge branch 'bugfix-for-amg-with-scalar-matrix' into 'master'

ref:core/dune-istl This bug is really new \-- it only came with the
introduction of support for scalar-valued matrices.

See merge request [!273]

  [!273]: gitlab.dune-project.org/core/dune-istl/merge_requests/273

This bug is really new -- it only came with the introduction of
support for scalar-valued matrices.

Merge branch 'implement-AMG-for-scalar-valued-matrices' into 'master'

See merge request [!272]

  [!272]: Nonecore/dune-istl/merge_requests/272

To make it easier to understand.

Simplify the code while we're there.

Is not used.

Merge branch 'implement-umfpack-for-scalar-matrices' into 'master'

See merge request [!271]

  [!271]: Nonecore/dune-istl/merge_requests/271

To prepare for testing with more matrix types.

Merge branch 'implement-superlu-for-scalar-valued-matrices' into 'master'

See merge request [!270]

  [!270]: Nonecore/dune-istl/merge_requests/270

There is no reason why it should be a C-pointer.

Previously, only BCRSMatrix<FieldMatrix<T,1,1> > was tested.

Previously, all code was in the specialization of that class
for BCRSMatrix<FieldMatrix>.  That was overly restrictive:
most of the code does not actually rely on the precise type
of the matrix.  As a first step towards allowing more general
matrix type we move all the code into the general class.

In the debug output, 'n' was used for the number of matrix columns.
However, 'n' is the number of columns of the FieldMatrix objects
that serve as matrix entries.