Checkout:
- PBGitRepository: add checkoutRefish:
- PBRefController: renamed checkoutRef: to checkout: and use new method in PBGitRepository
- add to the contextual menus for commits (it was already in the menu for refs)
- add "Checkout branch" checkbox to the Create Branch sheet
- store the state in the defaults
- tell the commitController to rearrangeObjects so that the refs highlight correctly (seems to only be a problem when going from a branch to a detached HEAD at the same commit)
Update the methods for creating a branch.
- create new class and xib PBCreateBranchSheet
- remove old addRef: methods and iVars from PBRefController
- remove old sheet from PBHistoryView.xib
- put the implementation method in PBGitRepository
- add a contextual menu item for commits
- shows an error sheet
- ask the commitController to rearrangeObjects to make sure the new branch is shown
- switch from using "update-ref" to "branch" so that branches starting at a remote branch will track automatically (or not depending on the repo's settings)