IMAP: better diagnostic for MODSEQ parsing
IMAP: parse 64bit MODSEQ and HIGHESTMODSEQ correctly

Thanks to Alberto Mardegan (mardy on IRC) for reporting. Shame on me for not
checking this properly from the beginning.
build: adding .dsc file for Debian 7
www: fix link to the release announcement

Thanks to Caspar Schutijser (cschutijser on IRC) for reporting.
Header cleanup
BURL: recognize a correct response code

I have no idea how come this has ever worked. Blame me. Thanks to Stephan Bosch
(S[r]us on IRC) for reporting.
GUI: respect KDE's settings for the monospace font in webkit and composer

refs #547
html: user-defined stylesheet shall be at the very end to allow custom overrides