We used to try loose objects first with sha1_object_info(), but packed
objects first with read_sha1_file(). Now, prefer packed objects over loose
ones with sha1_object_info(), too.

Usually the old behaviour would pose no problem, but when you tried to fix
a fscked up repository by inserting a known-good pack,

	git cat-file $(git cat-file -t <sha1>) <sha1>

could fail, even when

	git cat-file blob <sha1>

would _not_ fail. Worse, a repack would fail, too.
Signed-off-by: NJohannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: NJunio C Hamano <junkio@cox.net>