Use of branches for pull requests
We should recommend that people commit their patches to branches.
Its important that we support this, since if the openjdk approach is to commit a patch as a new commit, then hg's inability to delete changes stops us from pulling in the commits from upstream and merging the pull request.
This is also needed for people who are planning on opening multiple pull requests at the same time,
It might be the case that we just need to test this, and it works already. A documentation change is needed either way.