Use a real IRC object in some tests.

Additional functional tests of window.irc.IRC will need a full
object embedded in these tests, so make use of a real one rather
than an anonymous skeleton object.

While here, do some major CoffeeScript cruft cleanup.
Normalize channel names in window.irc.IRC.

They are always keyed by lower-case key, but many parts of external
code were arbitrarily accessing elements of the "channels" object
without case-folding. Make it an internal-only "_channels" object
wrapped by accessors for find/new/delete which manage the object's
internals.
Merge branch 'channel_normalization' into tvierling