rebase: remove $branch as synonym for $orig_head
rebase: remove $branch as synonym for $orig_head

The variables $branch and $orig_head were used as synonyms. To avoid
confusion, remove $branch. The name 'orig_head' seems more suitable,
since that is the name used when the variable is persisted.

Signed-off-by: Martin von Zweigbergk <4a0689660d2c85c65ee5252dabed282f8fad3a91@gmail.com>
Signed-off-by: Junio C Hamano <a6723cc3f76163bf7adb636a73ac3b0ceb3e6b9b@pobox.com>

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