Warn users about a dirty working directory.
If a user posts a change with no revision arguments, they probably want their

"current" state to be the change. We've had a little bit of confusion with Git

users who hadn't committed their changes to a branch and were upset that their

working tree wasn't posted (like it would be with svn, for example).
This change adds a warning when the user invokes rbt post without explicit

revision arguments and has a dirty working directory.

Posted this change with some other stuff in my working directory and saw the

warning.