Don't filter out FLAG_DELETED messages.

This can cause all kinds of problems in supporting this for both
CONDSTORE and non-CONDSTORE servers. If using ActiveSync and a MUA
that does NOT use a Trash folder (as EAS expects), then the trade
off is that messages flagged as \DELETED will still appear as
"normal" on the EAS client.
Use the '+' operator instead of array_intersect_keys here.

For non-CONDSTORE servers, this persists messages in state that have
fallen outside of the FILTER range for the client. Otherwise, if the
user deletes a message that has fallen outside of FILTER, the change
will never be picked up by the client. Need '+' instead of array_merge
since array_merge will reorder numerically indexed arrays.

Even when SOFTDELTE is implemented, there will be a small window of
time where a MUA may delete a message that has fallen outside of FILTER,
but before SOFTDELETE was sent to client.
Do not pollForChanges if we have imported any incoming changes.

Saves a potential backend ping on each collection.
No need to update any folder data on ping.