verify_uptodate(): add ce_uptodate(ce) test

verify_uptodate(): add ce_uptodate(ce) test

If we inside verify_uptodate() can already tell from the ce entry that
it is already uptodate by testing it with ce_uptodate(ce), there is no
need to call lstat(2) and ie_match_stat() afterwards.

And, reading from the commit log message from:

    commit eadb5831342bb2e756fa05c03642c4aa1929d4f5
    Author: Junio C Hamano <gitster@pobox.com>
    Date:   Fri Jan 18 23:45:24 2008 -0800

    Avoid running lstat(2) on the same cache entry.

this also seems to be correct usage of the ce_uptodate() macro
introduced by that patch.

This will avoid lots of lstat(2) calls in some cases, for example
by running the 'git checkout' command.

Signed-off-by: Kjetil Barvik <barvik@broadpark.no>
Signed-off-by: Junio C Hamano <gitster@pobox.com>