Stop using deprecated Gdk Thread API

[Alex Valavanis]

lp:inkscape r12027

Since Gtk+ 3.6. the Gdk threads API is deprecated [1]. Advice from the GDK 3 reference manual as follows:

"Instead of calling GTK+ directly from multiple threads, it is recommended to use g_idle_add(), g_main_context_invoke() and similar functions to make these calls from the main thread instead. The main thread is the thread which has called gtk_init() and is running the GTK+ mainloop. GTK+ itself will continue to use the GDK lock internally as long as the deprecated functionality is still available, and other libraries should probably do the same."

[1] http://developer.gnome.org/gdk3/unstable/gdk3-Threads.html

[Alex Valavanis (valavanisalex)]

Fix was committed in lp:inkscape r12690