[compiz] Allow core functions to be activated on hotcorners

[Sam Spilsbury]

Recently there was a suggestion that the "Show Desktop" plugin could
be activated on a hotcorner. I noticed that there is now a core
interface for this - otherwise known as "Hide all windows and focus
the desktop." This can be activated with Ctrl-Alt-D. However - it
cannot be activated with a hotcorner - which could be useful for
people who do not have a "Hide all windows and Show the desktop" on
thier panel. I then noticed that none of these options could be
activated with a hotcorner.

Is it possible to activate core funtions with a hotcorner?