Support MIME messages without alternative

It appears that MIME messages can have useful text in their root part,
this now parses them correctly.  I'm pretty sure the MIME parser is
now capable of completely subsuming the non-MIME parser, which should
probably happen...
Handle flags inside RFC822 IMAP requests

I guess it turns out there can be flags stuck inside the RFC822
response...  This now deals with them (it really just throws them
away).