[compiz] catch event when workspace is changing

[Mike Dransfield]

> With compiz, that code does not work because compiz use only one
> workspace (that is very very big). So how do you catch event when
> workspace is changing in compiz session? Python api would be nice, but
> C api is okay.
>

The event that is the viewport is changing, you should be able
to listen for XEvents and then filter the correct one.

It is one of my eventual aims to add internal events to compiz
for important things such as actions being triggered, special
or filtered X events (eg. window minimize, viewport change).
I would then like to send these out via dbus as signals so that
externals apps can detect them.

My earlier patches make the events possible, it is just a case
of adding the event triggers in the correct places and then
extending the dbus plugin so that it can forward the internal
events as dbus signals (possibly with some sort of registration
system so unnecessary signals are not sent).

This should make it much more straightforward for application
developers to integrate with compiz.