Detect deleted messages in ping() for non-CONDSTORE servers

We store the total number of messages per folder.
If a messages is deleted, the total number will change.
If a DELETE+ADD happens at the same time, UIDNEXT will still increase.

Note: I didn't increase the folder cache version on purpose.
Otherwise we lose the cached flags for no good reason.

Signed-off-by: Michael J Rubinsky <mrubinsk@horde.org>
Tweak comment.
phpdoc, cs
Ensure $data['t'] is actually available.
No need for the extra variable just use $status; Add logging.
No need for this for CONDSTORE servers.