pidgin/ljfisher-ssl-client-auth

Suppress error spews when we've left an IRC channel but the window is open.

My take on a patch from Florian Quèze to fix yet another IRC WHO problem.
For information on writing a plugin for Purple, Pidgin or Finch, go
http://developer.pidgin.im and click on API. From there, see the
HOWTOs in the "Related Pages" section.
You can also generate this documentation locally by installing
doxygen and graphviz dot, then running "make docs" in the
source tree. The documentation will be in the docs/html directory.