client-side-windows status update

[Alexander Larsson <alexl redhat com>]

More time has passed, and I've been slowly working on fixing whatever
issues pops up in my testing of the client side windows code. Its
looking pretty good now, and I run my whole desktop with it, including
metacity, panel, firefox, etc.

I updated the status at:
http://live.gnome.org/GTK%2B/ClientSideWindows

It lists the current known failures and unimplemented features. 

Richard has done some work on the quartz backend (some in the tree and
he has some local change), but there has been no work on the win32
backend. It would be nice if someone from the win32 team took a look at
this.

I think the client-side-windows part of the code is at a stage where it
could use a broader testing base. It mostly works, but small issues pop
up now and then when some app does a weird thing that have to be fixed.

The offscreen window part of the code has sort of bitrotted (although it
does compile) and will need some API changes and addition to work in the
latest design.

Maybe we can land this in early gtk+ 2.18, disabling the offscreen
window stuff from the public APIs (i.e. not installing headers) until it
is more finished. That way we can get people testing and fixing stuff.

This branch basically only changes the gdk/ directory, and thats
something that changes very rarely, so reverting the whole thing if we
find it too broken should be pretty easy.