update copyrights
use INT_MAX instead of zero for "no size limit"

this simplifies the actual conditions
don't unnecessarily use continue
add PassCmd option to query IMAP password dynamically

inspired by patches by
Aurélien Francillon <aurelien.francillon@eurecom.fr>,
Martin Stenberg <martin@gnutiken.se> and
sbfnk@users.sf.net.
make parse_list() callback based

this allows us to parse IMAP literals ({}) in every list.
allow the mailbox names in LIST responses to be literals

Lotus Domino seems to send them like that.
be somewhat stricter about the LIST response syntax

the first token *must* be a list.