added help message to rankfile mapper when failed if using alias instead of full hostname

This commit was SVN r21919.

orte/mca/rmaps/rank_file/help-rmaps_rank_file.txt

@@ -54,7 +54,8 @@ the provided rankfile.
 [bad-host]
 Rankfile claimed host %s that was not allocated or oversubscribed it's slots.
 Please review your rank-slot assignments and your host allocation to ensure
-a proper match.
+a proper match. Try using full hostname, ex: host1.openmpi.org instead of
+host1
 
 [bad-index]
 Rankfile claimed host %s by index that is bigger than number of allocated hosts.