named branches: improve pre-push logic (issue736)
Each named branch is considered separately, and the push is allowed if
no new branch heads are created for any named branch to be pushed.
Due to some tests's use of --debug, their output will change after this
addition. This has been fixed as well.
Co-contributor: Henrik Stuart <henrik.stuart@edlund.dk>
adding a/b/c/d/x
adding a/b/c/d/y
adding a/b/c/d/z
moving a/b/c/d/x to z/b/c/d/x
moving a/b/c/d/y to z/b/c/d/y
moving a/b/c/d/z to z/b/c/d/z