treeview: fix dragging of columns in mutter
treeview: fix dragging of columns in mutter

Don't recurse the mainloop in _gtk_tree_view_column_start_drag().
It doesn't serve any discernible purpose, and recursing the
mainloop from the flush-events phas of the frame clock breaks
frame synchronization with mutter.

https://bugzilla.gnome.org/show_bug.cgi?id=705176

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