git: check the correct remote branch for has_commit
git: check the correct remote branch for has_commit

Previously it was always checking against origin/$branch, but the
remote branch can have any name and the remote branch can also have
any name.

BobHood/liquidprompt,joshuarubin/dotfiles,pkkolos/liquidprompt,timhyson/liquidprompt,kenrachynski/liquidprompt,tocomo/liquidprompt,jonathanjsimon/liquidprompt,jaesivsm/liquidprompt,milouse/liquidprompt,dan-cleinmark/liquidprompt,dtschan/liquidprompt,lyoshenka/liquidprompt,laurentbardin/liquidprompt,joshuarubin/dotfiles,colinlieberman/liquidprompt,alexprengere/liquidprompt,tstone2077/liquidprompt,illwieckz/liquidprompt,joshuarubin/dotfiles,nojhan/liquidprompt,elementalvoid/liquidprompt,smadhueagle/liquidprompt,enrdstrm/liquidprompt,tsbarnes/liquidprompt,tkuminecz/liquidprompt,dpilone/liquidprompt,mathieumd/liquidprompt,joshuarubin/dotfiles