More flexible workflow: Always ask about renaming the branch if issue number not in name; always push to remote.
(Previously, it would only allow renaming if creating a new issue, and would blow up if you didn't rename and hadn't manually pushed)

- Change method of finding out current branch; works if branched from a local rather than remote branch
- more flexible issue number parsing
- Exit if pushing fails; sleep a bit to avoid suspected race condition
- Better test for whether to rename branch
- print what gets pushed