Core/messages: in_chan() checks for bot's nick. Was case sensitive, now isn't. Fixes a potential problem with the ! prefix in private messages on non-NetGamers IRCds.

Signed-off-by: Martin Stone <martin@d7415.co.uk>
(cherry picked from commit 0a1906ec5c20e5f5ec228a75809e2c1ead5c06f0)