As with Git, the Mercurial backend only posts changesets and ignores uncommitted changes. Warn users about this, since they may expect to be able to post the same output as 'hg diff'.

Ran 'rbt post' both with and without uncommitted changes.

I'm not sure if we want the '--deleted' flag included, since it's files that are tracked but have been deleted - e.g. using 'rm file' instead of 'hg rm file'.