Don't silently ignore bad reviewboardrc files.

Review Request #1156 — Created Oct. 6, 2009 and submitted

Eric Huss
This change causes post-review to print a friendly error message if you have a syntax error in your reviewboardrc file.  I had a typo in mine, and it took me a while to figure out why it was telling me it could not find a Review Board server.
Tested with a good and bad reviewboardrc file.
Christian Hammond
  1. Thanks. Committed on master (r56da9a1)