[Erc-help] making erc-hide-list apply to all messages

[Henrik E. <hen...@te...>]

Currently, erc-hide-list is only checked in the message handlers of a
small subset[1] of all possible messages.  It'd be nice to be able to
hide any message without having to resort to erc-insert-this and funky
regexps.

The attached patch moves the check to erc-display-message and removes
the checks from the handlers in erc-backend.el

[1] JOIN, KICK, MODE, NICK, PART, QUIT and TOPIC