merge: remove global variable head[]
merge: remove global variable head[]

Also kill head_invalid in favor of "head_commit == NULL".

Local variable "head" in cmd_merge() is renamed to "head_sha1" to make
sure I don't miss any access because this variable should not be used
after head_commit is set (use head_commit->object.sha1 instead).

Signed-off-by: Nguyễn Thái Ngọc Duy <024f400cd820cb2ddbe54c7fecfd01e45f30bb96@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