Add extra checks for GdkDevice functions that might fail on slave devices.
Add extra checks for GdkDevice functions that might fail on slave devices.

Documentation bits have been added as well.

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