[imp] IMAP parsing slowdown (really just preview & priority kill it)

[cpickert at t3inc.us]

Well, the attachment parsing doesn't slow anything down but the previews (i
suppose  inherently but, my machine should be 'very' fast) definitly DO. As
well the the priority colorization. Where can I start with trying to optimize
the preview parsing stuff? Zend Optimizer? ;) :)
I know it's not really 'IMAP' related but somewhat in nature.