Reverting r32355: a number of processes is not a notion that a low level
communication library should use to initialize itself.

Ralph will champion this change back with an RFC if there is a realistic
need/use case from the community.
usnic: do not call ompi_rte_abort()

Adapt to moving down to OPAL: find a PML-registered error callback,
and use that when we don't have a module context and we need to abort.

Failing that, just call exit().
usnic: fix a bunch of OMPI_* and ORTE_* constant usage

Somehow a bunch of OMPI_* and ORTE_* constants didn't get renamed in
the BTL move to OPAL.  This commit fixes that.
usnic: remove last vestiges of ORTE process names

These were missed when the BTLs moved to OPAL.
usnic: remove compatibility with v1.6 series

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.
usnic: remove all trailing whitespace

Style cleanup only; no code changes.
usnic: minor cleanup
usnic: check that connectivity pings came from where they said they came from

Ensure that incoming "ping" messages came from the IP address that
they think they came from.  If they don't, drop them (because it is
probably routing error), which will likely eventually cause the
connectivity checker to timeout, and therefore cause the job to abort.