How to disable slash commands

[Etan Reisner]

That option was removed as it served largely just to confuse and annoy
people, currently the way pidgin works is that on protocols without
"native" slash command support unknown slash commands are sent through,
whereas on protocols with "native" slash command support they are not (a
space before the slash will let it go through however). 

The protocols with native support are IRC, XMPP, and SILC.

    -Etan