This check was added to improve the error message returned when using
MPI without correctly initializing it (e.g. by creating a parallel
grid), see FS#1612 for further information.

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.

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

update documentation

[[Imported from SVN: r7086]]

see FS#1055 for details


[[Imported from SVN: r7055]]

[[Imported from SVN: r6925]]

[[Imported from SVN: r6678]]

This is part of FS 787

[[Imported from SVN: r6649]]

[[Imported from SVN: r6553]]

[[Imported from SVN: r6493]]

[[Imported from SVN: r6489]]

[[Imported from SVN: r6269]]

[[Imported from SVN: r6221]]

[[Imported from SVN: r6108]]

[[Imported from SVN: r6105]]

[[Imported from SVN: r5750]]

[[Imported from SVN: r5748]]

since the shared_ptr change?)

[[Imported from SVN: r5713]]

* update Makefiles and configure

[[Imported from SVN: r5643]]

[[Imported from SVN: r5631]]

[[Imported from SVN: r5604]]

[[Imported from SVN: r5603]]

Fixed parmetis check. Parmetis is only enanbled if the correct
CPPFLAGS are used (just like MPI).

[[Imported from SVN: r5573]]

make headercheck SILENT=1 CXXFLAGS="-Wall -pedantic":
* remove spurious ';'

[[Imported from SVN: r5380]]

[[Imported from SVN: r4968]]

[[Imported from SVN: r4923]]

[[Imported from SVN: r4779]]

Fixed a serious bug. (At least sum was not O.K. when working with an
inout array. We really have to allocate an out array and copy the
results.)

Made mpicollectivecommunication more generic and reduced code duplication.

There are to new functions (allreduce) than can be given a binary
function (e. g. std::plus) representing the calculation.

[[Imported from SVN: r4778]]

The collective operations now work with simple C arrays.

[[Imported from SVN: r4777]]

[[Imported from SVN: r4314]]

- no new documentation added. It just appears at new places.

[[Imported from SVN: r4297]]

if it is not needed.

Anyway the MPI error handler will be called before the error value is
returned. The default handler will abort the programm so the error
code will not be returned anyway.

[[Imported from SVN: r4080]]

Undone previous change.

[[Imported from SVN: r3868]]

[[Imported from SVN: r3866]]

two files. So, sequential applications do not try to include MPI even if HAVE_MPI is true

[[Imported from SVN: r3663]]

[[Imported from SVN: r3658]]

[[Imported from SVN: r3655]]