upload-pack: only accept commits from "shallow" line
upload-pack: only accept commits from "shallow" line

We only allow cuts at commits, not arbitrary objects. upload-pack will
fail eventually in register_shallow if a non-commit is given with a
generic error "Object %s is a %s, not a commit". Check it early and
give a more accurate error.

This should never show up in an ordinary session. It's for buggy
clients, or when the user manually edits .git/shallow.

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