Update compat.h to only handle compatability between v1.7/v1.8 and
v1.9/2.0 (i.e., the current trunk). Remove what seems to be the last
vestiages of OMPI/ORTE pollution in the now-OPAL-ized usnic BTL.
Currently use a hard-coded constant for the MCW size (i.e.,
MPI_COMM_WORLD size) for some initialization values in the v1.9/2.0
series; still need to figure out something better there.
This commit was SVN r32365.