Display error message if patch fails.

Review Request #336 — Created April 1, 2008 and submitted — Latest diff uploaded

Review Board SVN (deprecated)
I've noticed that the output from patch goes to stderr.  Every once in a while someone uploads some bizarre patch that fails to apply cleanly.  The error message is less than useful.  This fixes the problem.
Tested against a patch that was failing, and the error message was displayed as expected.  Also verified I didn't break good patches.