Git question: specify branches to push

[Stephen Berman <stephen.berman@gmx.net>]

I've pushed several commits to emacs-24 at Savannah, and each time git
says the following:

 ! [rejected]        master -> master (non-fast-forward)
error: failed to push some refs to 'srb@git.sv.gnu.org:/srv/git/emacs.git'
hint: Updates were rejected because a pushed branch tip is behind its remote
hint: counterpart. If you did not intend to push that branch, you may want to
hint: specify branches to push or set the 'push.default' configuration variable
hint: to 'simple', 'current' or 'upstream' to push only the current branch.

Of course I didn't want to push master so it's good it was rejected, but
it would be unpleasant if my master branch happens to be up to date when
I push emacs-24 (or vice versa).  But how do I tell git to push only
emacs-24 (or only master)?  I tried `git push emacs-24' and `git push
origin/emacs-24' but it didn't recognize either as an existing branch.

Steve Berman