Fixes bug 2134

diffs were being created for files where the area surrounding keywords
had changed, and the keywords were not being collapsed.  This was
happening for two reasons:
  * it couldn't understand paths with two leading slashes
  * `svn propget svn:keywords` can return strings with non-space delimiters

Also, I had submitted this previously as a pull request on github - sorry about that.
I couldn't find your policy for contributions, so I just figured that was it.  You might
want to make that a bit more visible.

Using reviewboard 1.5.5 on a Windows 7 server using Apache+mod_wsgi running on python 2.7 with subversion 1.6.15 (if that matters)