Support guessing review requests in rbt land.

Review Request #6713 — Created Dec. 31, 2014 and submitted — Latest diff uploaded

Information

RBTools
master
418968d...

Reviewers

rbt land now defaults to guessing review requests, unless using -r.
It will attempt to find a review request matching the specified branch,
or the current branch if one was not specified. It will prompt for a
match if unsure.

If a match is found, it will be used for the resulting commit message in
the merge.

Landed an actual change using --local and the branch name. Saw it find
the matching review request, merge, and push.