RFR: 296: git webrev fails

[Erik Helin]

Hi all,

please review this patch that sets the default value for `--rev` to
the parent of `origin..HEAD` (essentially the same as Mercurial's revset
expression `min(outgoing())^`).

Testing:
- Manual testing of `git-webrev` on Linux x64

Thanks,
Erik

-------------

Commit messages:
 - git-webrev: default to origin..HEAD for --rev

Changes: https://git.openjdk.java.net/skara/pull/506/files
 Webrev: https://webrevs.openjdk.java.net/skara/506/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/SKARA-296
  Stats: 13 lines in 1 file changed: 8 ins; 0 del; 5 mod
  Patch: https://git.openjdk.java.net/skara/pull/506.diff
  Fetch: git fetch https://git.openjdk.java.net/skara pull/506/head:pull/506

PR: https://git.openjdk.java.net/skara/pull/506