clone: drop connectivity check for local clones

clone: drop connectivity check for local clones

Commit 0433ad1 (clone: run check_everything_connected,
2013-03-25) added the same connectivity check to clone that
we use for fetching. The intent was to provide enough safety
checks that "git clone git://..." could be counted on to
detect bit errors and other repo corruption, and not
silently propagate them to the clone.

For local clones, this turns out to be a bad idea, for two
reasons:

  1. Local clones use hard linking (or even shared object
     stores), and so complete far more quickly. The time
     spent on the connectivity check is therefore
     proportionally much more painful.

  2. Local clones do not actually meet our safety guarantee
     anyway. The connectivity check makes sure we have all
     of the objects we claim to, but it does not check for
     bit errors. We will notice bit errors in commits and
     trees, but we do not load blob objects at all. Whereas
     over the pack transport, we actually recompute the sha1
     of each object in the incoming packfile; bit errors
     change the sha1 of the object, which is then caught by
     the connectivity check.

This patch drops the connectivity check in the local case.
Note that we have to revert the changes from 0433ad1 to
t5710, as we no longer notice the corruption during clone.

We could go a step further and provide a "verify even local
clones" option, but it is probably not worthwhile. You can
already spell that as "cd foo.git && git fsck && git clone ."
or as "git clone --no-local foo.git".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>