[RFC] Grab & relative motion

[Philipp Brüschweiler]

Hi everyone,

This small patch series implements a simple type of grab & relative
motion combination in both wayland and weston. For more details,
please look at the commit messages.

I'd be great to get some feedback on this, I'm not even sure if the
general direction of the protocol change & implementation is something
that could be merged into master some day ;)

Cheers,
Philipp