Puts the pull id in the prompt for the shell launched by github-merge.sh. This is useful as a reminder that you're a) in a special shell b) which pull you're working on.
user@asdf:/.../projects/bitcoin/bitcoin$ contrib/devtools/github-merge.sh 5427
Removing qa/rpc-tests/walletbackup.sh
Dropping you on a shell so you can try building/testing the merged source.
Run 'git diff HEAD~' to show the changes being merged.
Type 'exit' when done.
(5427)user@asdf:/.../projects/bitcoin/bitcoin$
The current solution is only triggered on Debian/Ubuntu, and makes use of the default PS1 building in .bashrc there. There may be a more general way, although I've tried overriding RC1 manually then bash --norc -i, but that completely replaces the prompt instead of adding to it.
