XI2 SD grabs

[Thomas Jaeger]

Hi Peter,

Sorry for bringing this up so late, I hadn't noticed this earlier
because easystroke is still causing mysterious server crashes. In commit
0c0ef42292f4c910c73b308cd75d77637312da53, you removed the code that was
responsible for detaching slave devices when a grab was activated to
bring things more in line with how XI1 grabs worked.  I'd argue that the
old XI2 way was the right way to go about things and that sending core
events during XI2 grabs is less than ideal:  The point of XI2 grabs is
to get complete control over the device; if other clients should still
receive events, it would suffice to select for events.  It is very
difficult right now for the grabbing client to ensure that other clients
don't receive any core events, at least in the case of passive grabs and
probably inherently racy.

I don't understand why gimp thinks it needs device grabs at all, but if
compatibility is an issue, I think it would be better to treat XI1 and
XI2 grabs differently and only detach the device for the latter.

Thanks,
Tom