Change git branch autocompletion to ignore prefix

[RyanBuck182]

At work, our branches are prefixed with something like refactor/ or docs/ or feature/. However, I want branch autocomplete to just ignore this and match to the part after the prefix.

[RyanBuck182]

Or maybe only have it match up to the /, then the user types a little more and it can match after it? (similar to directories)