QPID-4975: Only send correlation id if it isn't empty.

git-svn-id: https://svn.apache.org/repos/asf/qpid/trunk@1499540 13f79535-47bb-0310-9956-ffa450edef68
QPID-4627: Implement most  of the remaining selector special identifiers
Implemented:
  message_id, correlation_id,
  jms_type, creation_time, absolute_expiry_time

There are a couple of caveats: The easily available way to get
jms_type doesn't distinguish between an empty string and the
property not being sent at all. So we treat this case as property
not set as that seems like it will get most cases correct (why bother
to send an empty jms_type?). The creation_time property is currently
implemented as the time the message was put on the queue (if enabled
in the broker) as amqp 0_10 has no standard way to indicate the
creation time and we're not currently holding the creation time for amqp 1.0
messages.