rebase: do not get confused in fast-forward situation.
rebase: do not get confused in fast-forward situation.

When switching to another branch and rebasing it in a one-go, it
failed to update the variable that holds the branch head, and
did not detect fast-forward situation correctly.

Signed-off-by: Junio C Hamano <dc50d1021234060e53ec42a77d526afa2fe07479@cox.net>

destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git,destenson/git