ui/gtk.c: do not use gdk_display_warp_pointer when GTK ver >3.0

ui/gtk.c: do not use gdk_display_warp_pointer when GTK ver >3.0

Commit 9697f5d2d38e5dd1e64e8e0d64436e6d44e7b1fe "gtk: custom cursor support"
introduced unconditional usage of gdk_display_warp_pointer(). This function
is marked as deprecated since GTK-3.0, and triggers warning (error with -Werror)
during compilation.
Conditionally change gdk_display_warp_pointer() method usage to gdk_device_warp
usage, as suggested by compiler.

Signed-off-by: Igor Mitsyanko <i.mitsyanko@gmail.com>
Message-id: 1368197985-44608-1-git-send-email-i.mitsyanko@gmail.com
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>