git-cvsserver: run post-update hook *after* update.

git-cvsserver: run post-update hook *after* update.

CVS server was running the hook before the update action was
actually done. This performs the update before the hook is called.

The original commit that introduced the current incorrect behavior
was 394d66d "git-cvsserver runs hooks/post-update". The error in
ordering of the hook call appears to have gone unnoticed, but since
git-cvsserver is supposed to emulate receive-pack, it stands to
reason that the hook should be run *after* the update. Since this
behavior is inconsistent with recieve-pack, users are either:

  1) not using post-update hooks with git-cvsserver;
  2) using post-update hooks that don't care whether they are
     called before or after the actual update occurs;
  3) using post-update hooks *only* with git-cvsserver, and
     relying on the hook being called just before the update.

This patch would affect only users in case 3. These users are
depending on fairly obviously wrong behavior, and moreover they can
simply change their current post-update into post-recieve hooks,
and their systems will work correctly again.

Signed-off-by: Stefan Karpinski <stefan.karpinski@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>