Instead of checking reachability from the refs, you can ask
fsck to check from a particular set of heads. However, the
error checking here is quite lax. In particular:
1. It claims lookup_object() will report an error, which
is not true. It only does a hash lookup, and the user
has no clue that their argument was skipped.
2. When either the name or sha1 cannot be resolved, we
continue to exit with a successful error code, even
though we didn't check what the user asked us to.
This patch fixes both of these cases.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>