Encode the MPI version in SAMRAI_config.h

[drwells]

This would have saved us some trouble recently with a user who compiled SAMRAI with one MPI version and IBAMR with another - this is the only dependency with which we cannot detect multiple MPI versions since SAMRAI is statically linked. We can get 99% of the way there, however, by duplicated PETSc's "check that we have the right MPI version and MPI implementation" logic in the header.