Log Message:
Update parallel/pdsh to 2.31.

* Changes in pdsh-2.31 (2013-11-07)
===================================
 -- Fix issue 56: slurm: Allow mixed use of -P, -w and -j options.
 -- Fix issue 59: pdsh very slow when using a few thousand hosts
    and genders.
 -- testsuite: Expanded tests for genders module (Pythagoras
    Watson)

* Changes in pdsh-2.30 (2013-03-02)
===================================
 -- Fix issue 55: genders -X option removes more hosts than
    expected.
     (This was a generic fix for hostname matching, so it probably
      affected -x and other options as well.)
 -- testsuite: Add test for issue 55.