Require the feed url and item url parameters to svn2feed.py, otherwise we create feeds with empty atom:id elements, which is pretty lame.
Require the feed url and item url parameters to svn2feed.py, otherwise
we create feeds with empty atom:id elements, which is pretty lame.

* contrib/hook-scripts/svn2feed.py
  (main): Initialize item_url and feed_url to None, and check for that
   later on to ensure that they've been specified at the command line.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion