Although this is not the solution you requested, I'd like to hint at another way to cover this, with a commit hook :
You can put in .git/hooks a commit-msg file with these contents :
#!/bin/bash
current_branch="$(git rev-parse --abbrev-ref HEAD)"
tmp=$(mktemp) || exit
echo "$current_branch $(cat "$1")" > "$tmp"
mv "$tmp" "$1"
(Thanks guys for the improvements in bash syntax made with your help here)
Then it would automatically prepend your commit messages with the branch name, which does the trick in JIRA.
For the rare occasions when you'd prefer NOT to trigger the hook, do this :
git commit -n -m"Your message"
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