Posting and stamping made use of some of the new utility functions that

were pulled out of rbt post. Each of these utility functions ended up

calling get_revisions(), which, in the case of Git, could cause the same

warning about pending changes in the working directory to be displayed.
There was really one major utility function that needed to be called,

and it was calling other utility functions that each called

get_revisions(). Now the main utility function, used for guessing review

requests, takes the revisions as an argument, ensuring we only ever

perform that logic once.
Along with fixing the warning, this should also speed things up a little

bit by reducing the number of calls that need to be made to other

command line apps, such as git.

Posted this change, along with some modified files not staged for commit.

Only saw one message.
Then I posted again with rbt post -u. Only saw the message once, not twice.
Ran rbt stamp against this review request. Worked fine.
In debug mode, I didn't see extra invocations of git.
Unit tests pass.
Pyflakes had nothing to complain about.