Thinking about popup windows

[Rob Bradford]

This and the patches for weston are an attempt at how a client could
communicate with the compositor about positioning surfaces. The slightly weird
thing is that you make this request not against the surface you are going to
position but against its parent.

This makes the implementation in the client side a little bit weird since you
have to store the surface that you are going to do the work on - perhaps we
should adjust the protocol so you pass the parent into the request and make
the request on the surface you are going to position.

Cheers,

Rob