IMAP Gateway: system flags (rough effort 1,5 days)

[Andreas Hügel]

Flags Message Attribute

   A list of zero or more named tokens associated with the message. A
   flag is set by its addition to this list, and is cleared by its
   removal. There are two types of flags in IMAP4rev1. A flag of
   either type can be permanent or session-only.

   A system flag is a flag name that is pre-defined in this
   specification. All system flags begin with "\". Certain system
   flags (\Deleted and \Seen) have special semantics described
   elsewhere. The currently-defined system flags are:

        \Seen
           Message has been read

        \Answered
           Message has been answered

        \Flagged
           Message is "flagged" for urgent/special attention

        \Deleted
           Message is "deleted" for removal by later EXPUNGE

        \Draft
           Message has not completed composition (marked as a draft).

        \Recent
           Message is "recently" arrived in this mailbox. This session
           is the first session to have been notified about this
           message; if the session is read-write, subsequent sessions
           will not see \Recent set for this message. This flag can not
           be altered by the client.

           If it is not possible to determine whether or not this
           session is the first session to be notified about a message,
           then that message SHOULD be considered recent.

           If multiple connections have the same mailbox selected
           simultaneously, it is undefined which of these connections
           will see newly-arrived messages with \Recent set and which
           will see it without \Recent set.

   A keyword is defined by the server implementation. Keywords do not
   begin with "\". Servers MAY permit the client to define new keywords
   in the mailbox (see the description of the PERMANENTFLAGS response
   code for more information).

   A flag can be permanent or session-only on a per-flag basis.
   Permanent flags are those which the client can add or remove from the
   message flags permanently; that is, concurrent and subsequent
   sessions will see any change in permanent flags. Changes to session
   flags are valid only in that session.

        Note: The \Recent system flag is a special case of a
        session flag. \Recent can not be used as an argument in a
        STORE or APPEND command, and thus can not be changed at
        all.

Current state:
- \Seen, \Flagged and \Deleted are working properlly
- \Answered does not work due to a problem with the setMessageStatus/getMessageStatus methods in TxC.
- freely defined Flags can be handled the same way \Deleted was handled