rootless mode

[Robert Collins]

I've been thinking about rootless mode.

Here's  my current thoughts:

1) We create a real win32 window for each X window. 
2) We use SetWindowLong to store the X window pointer in the WIN32
struct, so that when a message arrives to that windowclass's WindowProc,
we can lookup the X window the message belongs to.
3) We use WindowPrivates to store the WIN32 related window HANDLE and
other gunk.

I don't know how we go about telling X it's rootless - Alan, I'm hoping
you can jump in here and say 'do X, Y and Z'.

Anyway, whilst I won't have time to be a significant contributor, I hope
to have a proof-of-concept patch against the Native GDI engine shortly.

Rob