Fixes for opal_path_nfs():

 * Fix some typos in macro names.
 * Add case for OS's that have statfs() but no struct statfs (!).
 * Add case for NetBSD with struct statvfs.f_fstypename.

Many thanks to Paul Hargrove who developed the majority of this patch.

Reviewed by Jeff Squyres.

cmr=v1.7.4:reviewer=ompi-rm1.7