bug in bash completion for git-branch --set-upstream-to on OSX

[Jason Karns <karns.17@gmail.com>]

There appears to be a bug in the bash completion for git-branch when
attempting to complete the remote ref argument for --set-upstream-to=

When:

$ git branch --set-upstream-to=origin/mast<TAB>

I would expect it to complete to:

$ git branch --set-upstream-to=origin/master

However, the completion for --set-upstream-to= completes the ref
correctly, but completely wipes the --set-upstream option; resulting
in:

$ git branch origin/master


I'm running on OS X 10.9.5 with git from homebrew:
$ bash --version
GNU bash, version 4.3.33(1)-release (x86_64-apple-darwin13.4.0)
$ git --version
git version 2.3.3

The same behavior does *not* manifest (it works as expected) on CentOS
6.5, bash 4.1.2.1 (GNU bash, version 4.1.2(1)-release
(x86_64-redhat-linux-gnu)). I'm running git 2.0.3 on CentOs but
sourcing the shell completion script from latest source: 9ab698f

I also cloned down latest git source on OS X and the bug still
manifests when sourcing the completion script at 9ab698f.

~ Jason