[WIP] pstream comunicator does not get released

run any case with valgrind. You'll get:

==25576==    by 0x9D3A7DC: Foam::UPstream::allocatePstreamCommunicator(int, int) (in /export/preston2/mattijs/OpenFOAM/work/develop/openfoam/platforms/linux64GccDPInt32Opt/lib/openmpi-system/libPstream.so)
==25576==    by 0x8284E5C: Foam::UPstream::allocateCommunicator(int, Foam::List<int> const&, bool) (in /export/preston2/mattijs/OpenFOAM/work/develop/openfoam/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so)
==25576==    by 0x8638BA3: Foam::globalMeshData::updateMesh() (in /export/preston2/mattijs/OpenFOAM/work/develop/openfoam/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so)
==25576==    by 0x8638FED: Foam::globalMeshData::globalMeshData(Foam::polyMesh const&) (in /export/preston2/mattijs/OpenFOAM/work/develop/openfoam/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so)
==25576==    by 0x8672AA7: Foam::polyMesh::globalData() const (in /export/preston2/mattijs/OpenFOAM/work/develop/openfoam/platforms/linux64GccDPInt32Opt/lib/libOpenFOAM.so)
==25576==    by 0x56E5D14: Foam::fvMesh::lduAddr() const (in /export/preston2/mattijs/OpenFOAM/work/develop/openfoam/platforms/linux64GccDPInt32Opt/lib/libfiniteVolume.so)

Marked as WIP since might be solved already in feature-localWorld.