This change uses GCD to schedule certain git commands for background execution. All background commands occur on the queue returned by PBGetWorkQueue(), and the results are executed on the main queue. This results in a dramatic improvement in the performance of reloadRefs when there are lots of tags. More improvements are possible with this approach, this is just something to get things rolling.
…riginally belonged to old git-svn remotes. * Added helpText property to PBGitSVOtherRevItem
Conflicts: PBGitHistoryController.h PBGitWindowController.h