SECURITY NOTE: if you deleted or renamed a pubkey file after 5fd9328
went in (April 12th), please:

  - upgrade asap, then
  - go to your latest gitolite-admin clone and "git push -f"

Otherwise this is not urgent.

5fd9328 (and its minor successor 813a2a9) were about preventing the
gitolite admin from sneaking in files to src/ and hooks/ into
$GL_ADMINDIR.  It seemed easy enough to do this by converting the
path-less checkout to a with-paths checkout, but this has caused a worse
problem -- deleting a keydir/foo.pub now no longer has an effect; the
file still hangs around in the work tree.

Ouch!  (and thanks to teukka for noticing)

We now do this check as a separate step, so the checkout can revert to
being path-less.