Use patch files instead of diff files for binaries

PR requests with binary additions will fail to apply the diff with the 
following error:

  error: cannot apply binary patch to '...' without full index line

The patch supplied by github has all the requisit information that the diff is
missing.

- use the PATCH_URL instead of the DIFF_URL

See: http://build.monkeypuppetlabs.com:8080/job/GIT-Pull-Request/788/consoleFull