Correctly use GtkApplication 'activate' signal, fix 'withdrawn' mode

At startup, if the application was in 'withdrawn' mode, that is, wasn't
supposed to show up until the user clicks on the tray icon (if present),
the application used to block completely, due to a lack of Gdk locks in
the "activate" signal of the GtkApplication's handler: this signal comes
from the GApplication object, which isn't aware of the Gdk lock and
thus, doesn't hold it while running the handler, contrary to what's
happening during "normal" Gtk events.

Or that's what I understood.

Fix #57

CHANGELOG

@@ -5,6 +5,8 @@ Bug fixes
 '''''''''
 
     * fix crashs on Gtk.TextView when updating the lyrics of a song
+    * fix withdrawn mode by fixing incorrect usage of threads and Gtk
+      eco-system
 
 
 1.7a2 (2013-11-26)

sonata/launcher.py

@@ -164,6 +164,7 @@ class FakeModule:
 
 
     def on_application_activate(application):
+        Gdk.threads_enter()
         windows = application.get_windows()
 
         if windows:
@@ -172,7 +173,7 @@ def on_application_activate(application):
         else:
             sonata = main.Base(args)
             sonata.window.set_application(application)
-            sonata.window.show()
+        Gdk.threads_leave()
 
     app = Gtk.Application(application_id="org.MPD.Sonata")
     app.connect("activate", on_application_activate)