Fix for current Weston.

[vanfanel]

Current Weston doesn't have weston_watch_process() but wet_watch_process() which requires both the process and the compositor.

Since the data pointer was used to pass the command to run, I had to modify the binder data struct to accomodate the compositor there, etc.

[keithbowes]

I wasn't sure if they were the same or different (weston.h is extremely underdocumented), but I put an ifdef in my fork regardless. I was wondering if perhaps I could just use weston_client_launch, replacing the lower-level use of system_nowait, but I just went the safer route of less breakage.

[selurvedu]

Your fork works, thank you.