quartz: Check if a drag ends inside a known window
quartz: Check if a drag ends inside a known window

If a drag ends inside a known window, set the dest_window field
in the drag context. This information is needed to implemented
notebook tab dragging.

https://bugzilla.gnome.org/show_bug.cgi?id=752638

Distrotech/gtk,Distrotech/gtk,Distrotech/gtk,Distrotech/gtk,Distrotech/gtk