[Downloader::Git] Skip cache pull if ref is available.
[Downloader::Git] Skip cache pull if ref is available.

mglidden/CocoaPods,Ashton-W/CocoaPods,orta/CocoaPods,vivekshukla-mob-ibtech/Repository,ashfurrow/CocoaPods,mglidden/CocoaPods,0xced/CocoaPods,mglidden/CocoaPods,segiddins/CocoaPods