Add two	predefined MPI object padding tests:

 1. Canary compile-time test: this is compiled whenever you compile
    the entire OMPI tree.  It's a noinst standalone library comprised
    of a single .c file, so no one will notice its addition, and it
    doesn't get linked/installed to any real build products.  If we
    are out of padding space on any predefined MPI object type, it
    will fail to compile.  This will alert/annoy a human, who will be
    able to fix the real problem.
 1. Added a "make check" test that will print out the amount of
    predefined padding left on all the MPI object types.