[mms] More accurate way of determining appended UID on append when UIDPLUS is not available.

Since Message-IDs can be duplicated within a mailbox (if more than one
copy of same message exists), we want the highest UID.
Thought so, but wanted to check
Abstract message ID search into separate method
[mms] Horde_Mime_Headers#parseHeaders() now accepts resources and Horde_Stream objects.
Have Horde_Mime_Headers#parseHeaders() deal with all parsing details
Pass stream in
Another place to pass in a stream
[mms] Add 'force_map' option to Horde_Imap_Client_Base#copy() to guarantee that the mapping array is always returned.

See Bug #13010