mpi4py: add a class to convert communicators

This will allow mpi4py and VTK to use each others MPI communication
sets.

Change-Id: I7b9d297ec833b71507b92aac374335e6271f1f59
wrapping: check for Tcl wrapping exclusion for warnings

Don't warn if the module isn't wrapped for Tcl explicitly.

Change-Id: Iba520319f810938e6e60ff39475cbde736543786
Merge topic 'mpi4py-communicator' into master

8e09aec2 wrapping: check for Tcl wrapping exclusion for warnings
09edf3fd mpi4py: add a class to convert communicators