[[Imported from SVN: r4968]]

[[Imported from SVN: r4925]]

[[Imported from SVN: r4923]]

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]]

[[Imported from SVN: r4314]]

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

[[Imported from SVN: r4297]]

[[Imported from SVN: r4291]]

[[Imported from SVN: r3801]]

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]]

[[Imported from SVN: r3615]]

- provides sum/product/min/max for any value type with operator+, operator* and operator <
  in a generic way using MPI Operators ans MPI data types. Really nice :-)
- Default version provides dummy communication functions. Can be used to
  make sequential versions compile without MPI
- It would be possible to include also point to point communication to have
  a nice way to avoid including mpi.h everywhere.

[[Imported from SVN: r3614]]