Coding style
ShortcutHandler: remove unused method which is broken with Qt 4.6

QIcon::name was only added in Qt/4.7. Given that this method was not used by
Trojita at all, removing it is a bit cleaner than adding empty QString (and
therefore possibly breaking icons later on?) on ancient Qt.

CCMAIL: glad.deschrijver@gmail.com
IMAP: Better error reporting
IMAP: accept NIL when looking for unsigned ints

Thanks to Ashley Penney <apenney@gmail.com> (ashp on IRC) for reporting.

This is apparently required for broken IMAP servers like the "davmail" gateway
to Exchange(tm). Getting NIL is roughly as bad as -1 or -2 which we already
handle, so there's no reason for complaying so loudly in this case.