Only listen for mouse events from master devices
Only listen for mouse events from master devices

XInput2 has a concept of master and slave devices,
where a slave device is the actual physical device,
attached to a master device representing the cursor or keyboard
focus.

See http://who-t.blogspot.co.uk/2009/05/xi2-recipes-part-1.html

Mouse events were being received from both the master and slave
devices, but we are only interested in events from the master device.

Fixes #533

ozkriff/glutin,mitchmindtree/glutin,mneumann/glutin,notriddle/glutin,servo/glutin,vberger/glutin,Jayflux/glutin,TimNN/glutin,paulrouget/glutin,mvdnes/glutin,adambadawy/glutin,mmatyas/glutin,nox/glutin,nc4rrillo/glutin,tempbottle/glutin,vvuk/glutin,bvssvni/glutin,tomaka/winit,mbrubeck/glutin,ecoal95/glutin,retep998/glutin,tomaka/glutin,mbrubeck/glutin,fkaa/glutin,kornholi/glutin,Ms2ger/glutin