send-pack: forbid pushing from a shallow repository

send-pack: forbid pushing from a shallow repository

send-pack can send a pack with loose ends to the server.  receive-pack
before 6d4bb38 (fetch: verify we have everything we need before
updating our ref - 2011-09-01) does not detect this and keeps the pack
anyway, which corrupts the repository, at least from fsck point of
view.

send-pack will learn to safely push from a shallow repository later.

Signed-off-by: Nguyễn Thái Ngọc Duy <redacted>
Signed-off-by: Junio C Hamano <redacted>