combobox: popdown the combobox when on 'grab-broken-event'
combobox: popdown the combobox when on 'grab-broken-event'

And also explicitly remove pointer/keyboard grabs from the display.

Whenever the grab is reported lost, we should popdown the combobox, so that the
GDK_WINDOW_TEMP window is hidden and removed from the toplevel, as done with
the menu for example.

Leaving the GDK_WINDOW_TEMP window open when re-activating the application
triggers several issues in the win32 backend, due to restacking windows of the
non-toplevel group into the toplevel group:

https://bugzilla.gnome.org/show_bug.cgi?id=695200

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