Added a test for the Gtk3 UI integration, following the Gtk2 pattern.

docs/examples/lib/gui-gtk3.py

@@ -0,0 +1,37 b''
+#!/usr/bin/env python
+"""Simple Gtk example to manually test event loop integration.
+
+This is meant to run tests manually in ipython as:
+
+In [1]: %gui gtk3
+
+In [2]: %run gui-gtk3.py
+"""
+
+from gi.repository import Gtk
+
+
+def hello_world(wigdet, data=None):
+    print "Hello World"
+
+def delete_event(widget, event, data=None):
+    return False
+
+def destroy(widget, data=None):
+    Gtk.main_quit()
+
+window = Gtk.Window(Gtk.WindowType.TOPLEVEL)
+window.connect("delete_event", delete_event)
+window.connect("destroy", destroy)
+button = Gtk.Button("Hello World")
+button.connect("clicked", hello_world, None)
+
+window.add(button)
+button.show()
+window.show()
+
+try:
+    from IPython.lib.inputhook import enable_gtk3
+    enable_gtk3()
+except ImportError:
+    Gtk.main()