Do not modify associated device for non-master devices on dispose
Do not modify associated device for non-master devices on dispose

Only master devices must modify the associated device to separate
a pointer/keyboard pair, slave devices must only call
_gdk_device_remove_slave().

Fixes bug 639767 - password not accepted in gnome-screensaver dialog,
reported by Frederic Crozat. On VT-switch, the X server removes its
grab on HW devices, the effect on clients is that slave devices
disappear, and these were mistakenly mangling the master device
hierarchy. so gdk_device_get_associated_device() on the client
pointer wouldn't return the paired keyboard anymore.

The final effect is that gtkplug-x11 wasn't setting a keyboard to
its generated events.

ebassi/gtk,Adamovskiy/gtk,alexlarsson/gtk,Lyude/gtk-,grubersjoe/adwaita,chergert/gtk,grubersjoe/adwaita,alexlarsson/gtk,jadahl/gtk,Lyude/gtk-,davidt/gtk,bratsche/gtk-,jigpu/gtk,grubersjoe/adwaita,ahodesuka/gtk,simokivimaki/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,ebassi/gtk,simokivimaki/gtk,chergert/gtk,bratsche/gtk-,Lyude/gtk-,chergert/gtk,davidgumberg/gtk,ahodesuka/gtk,msteinert/gtk,ebassi/gtk,simokivimaki/gtk,grubersjoe/adwaita,jessevdk/gtk,alexlarsson/gtk,alexlarsson/gtk,jessevdk/gtk,davidgumberg/gtk,ebassi/gtk,ahodesuka/gtk,Lyude/gtk-,Distrotech/gtk2,simokivimaki/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,Sidnioulz/SandboxGtk,Adamovskiy/gtk,msteinert/gtk,ahodesuka/gtk,Distrotech/gtk2,Sidnioulz/SandboxGtk,bratsche/gtk-,chergert/gtk,davidt/gtk,jadahl/gtk,davidt/gtk,davidt/gtk,alexlarsson/gtk,chergert/gtk,davidt/gtk,grubersjoe/adwaita,bratsche/gtk-,davidgumberg/gtk,bratsche/gtk-,jessevdk/gtk,ahodesuka/gtk,Lyude/gtk-,jigpu/gtk,davidt/gtk,jadahl/gtk,simokivimaki/gtk,grubersjoe/adwaita,jigpu/gtk,ahodesuka/gtk,jadahl/gtk,msteinert/gtk,jessevdk/gtk,jessevdk/gtk,Adamovskiy/gtk,jigpu/gtk,alexlarsson/gtk,Lyude/gtk-,Sidnioulz/SandboxGtk,alexlarsson/gtk,jigpu/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,jigpu/gtk,jigpu/gtk,Sidnioulz/SandboxGtk,ebassi/gtk,davidgumberg/gtk,Lyude/gtk-,ebassi/gtk,jessevdk/gtk,Adamovskiy/gtk,davidgumberg/gtk,jigpu/gtk,msteinert/gtk,jadahl/gtk,Adamovskiy/gtk,jadahl/gtk,Distrotech/gtk2,jadahl/gtk,davidgumberg/gtk,grubersjoe/adwaita,Adamovskiy/gtk,chergert/gtk,Distrotech/gtk2,ahodesuka/gtk,alexlarsson/gtk,msteinert/gtk,Distrotech/gtk2,msteinert/gtk,Adamovskiy/gtk,Adamovskiy/gtk,grubersjoe/adwaita,Distrotech/gtk2,ahodesuka/gtk,Lyude/gtk-,bratsche/gtk-,simokivimaki/gtk,jessevdk/gtk