Sample UIDs in SELECT $mailbox (QRESYNC ...) commands.

Sample UIDs in SELECT $mailbox (QRESYNC ...) commands.

This should avoids most false-positive among messages reported as
VANISHED by the server but unknown from the database.  The reason for
this server behavior is that QRESYNC [RFC7162] doesn't force the server
to remember the MODSEQs of EXPUNGEd messages.  By passing a sample of
known UIDs/sequence numbers we let the server know that the messages
have been EXPUNGEd [RFC7162, section 3.2.5.2].