#117 IMAP needs to keep better track of state

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On an IMAP server, a message may have as many states as a client dictates to it. And to faciliate for this, I have to change the code in IMAP to first clear any states a message may have, and then set the appropriate state on the message in question, so it is the only state. I guess I'll do this, but if anyone wants to help me feel free... (libcronosII/imap.c)