Move opal_portable_platform.h to opal/include/opal, which is where it really
should have been all along and fix one place that uses the file

Update opal_portable_platform.h with changes to mpi_portable_platform.h made 
in r29608.

Make mpi_portable_platform.h a symlink to opal_portable_platform.h, so that
they won't get out of sync.  I'd like to remove mpi_portable_platform.h, but
we don't automatically add -I${includedir}/openmpi/ to make that sane from
a header include point of view, so that's future work.
update ignore file