This very old gcc bug https://gcc.gnu.org/bugzilla/show_bug.cgi?id=10200 is fixed in clang but not in icc or gcc, see FS#1505.

In order to simplify fallback handling between code with and without MPI
support, this patch makes the specialization of CollectiveCommunication
for MPI communicators default-constructible by defaulting the underlying
MPI communicator to MPI_COMM_WORLD, which should be reasonable for most
scenarios.

As the non-specialized version for sequential code is already
default-constructible, this allows grid constructors to accept a
CollectiveCommunication object regardless of whether MPI support is
enabled or not and to provide a default value for this parameter.

This patch resolves FS#1497.

CollectiveCommunication serves as a fallback implementation, when
code that is written for parallel computations is executed in sequential.
The template parameters BinaryFunctions are no-op then, but they are
still there to define the interface. However, in a generic (parallel)
implementation these will be given. Including binaryfunctions.hh here
avoids error messages due to no-op template parameters whose names
could not be found by the compiler.

These headers were moved in Dune 2.3.

when we try to send data, it might happen, that for some reason we don't want to any data.
This happens, when the dynamic size of our CommPolicy is 0. In that case we must not add a
MessageInformation, otherwise we get an MPI error.

Somehow, the vector version of CollectiveCommunication< MPI_Comm >::prod
passed std::plus to allreduce (instead of std::multiplies). This patch
corrects this flaw.

VariableSizeCommunicator now appears in doxyen and the parallel
index sets are a subsection of the parallel section.

There entries in doxyerror.log about undocumented function
parameters and parameters that had a wrong name in the documentation.
This patch fixes this.

This patch introduces a new macro DUNE_UNUSED_PARAMETER(parm) for marking
unused parameters that are there for a purpose (e.g. the prescribed interfac
The macro simply performs a cast to void. In addition all unused parameter w
that I found were removed.

With this patch VariableSizeCommunicator now really supports a varying number of data entries
per index during communication.

[parallel,release] Adds a new buffered communicator that does not need to know the data amount per index when receiving.

During communication of data with a parallel DUNE grid the amount of data items
received at an index is not known at the receiving side. With this communicator
it is possible to build such a communication based on index lists at the sending
and receiving side. With this patch only fixed size of data items per index is
supported.

There was one line of diff missing in that patch. Sorry!

Previously, copying a RemoteIndexListModifier resulted in a double
free of a pointer to a list of global indices. There was no need to
use a pointer to this, though. After this patch we store the list directly
by value. Thus the default copy constructor works but makes a rather cheap copy
of a (most often empty) singly linked list and we get rid off the non-default
destructor.

Previously, a variable (found) was only initialized in one branch
of an if statement but used later on in any case. This patch makes
sure that is initialized in both branches.

update documentation

Patch by Bernd Flemisch

[[Imported from SVN: r7385]]

add missing implementation of state()

[[Imported from SVN: r7378]]

[[Imported from SVN: r7124]]

[[Imported from SVN: r7099]]

[[Imported from SVN: r7092]]

[[Imported from SVN: r7087]]