[winswitch] support for warping pointer

[Fazlul Shahriar]

Hi,

I'm trying to use the acme text editor in xpra, which makes heavy use of
pointer warping but the warping functionality doesn't seem to work. Here is
a video of how acme warps the pointer when opening a file:
http://youtu.be/dP1xVpMPn8M?t=9m28s

It looks like acme is using the XWarpPointer(3) function, so perhaps xpra
doesn't support this function?

Thanks,
fhs