Update to 1.31

Upstream changes:
1.31 (2012/11/17)
            (ms) To better deal with the race condition in the
                 previous release, kill the newly created child
                 process first, then send a killpg to its process
                 group and ignore the outcome.

            (ms) [RT 81203] Jim A Kessler reported a perl 5.16 issue
                 with the "AutoLoader" line, so I went ahead and removed
                 all references to "Exporter" and "AutoLoader", as
                 Proc::Simple isn't using them at all.


(wen)