Adding THREAD=References support

Really basic, not ready for prime time at all. Awful use of .replace and
eval for just proof of concept "does this work as intended?". The answer
is yes (and it does what it sets out to do... just needs rewriting ;)
Fixing undefined bodies on blank email

Fetching an email that was unread (and subsequently marked as read) a
second time would result in a fatal error on line 356 - cannot read
property 'length' of undefined.

parsers.parseFetchBodies could return bodies as undefined, bodies now
inits as array.