[pitivi] effects: Hide GdkPixbufOverlay

[Thibault Saunier <tsaunier src gnome org>]

commit ac7a797196e1125c45b25869d55826806690ac64
Author: Alexandru Băluț <alexandru balut gmail com>
Date:   Tue Jan 12 15:08:59 2016 +0100

    effects: Hide GdkPixbufOverlay
    
    Reviewed-by: Thibault Saunier <tsaunier gnome org>
    Differential Revision: https://phabricator.freedesktop.org/D670

 pitivi/effects.py |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)
---
diff --git a/pitivi/effects.py b/pitivi/effects.py
index d312e8d..f029811 100644
--- a/pitivi/effects.py
+++ b/pitivi/effects.py
@@ -271,7 +271,11 @@ class EffectsManager(object):
 
 
 # ----------------------- UI classes to manage effects -------------------------#
-HIDDEN_EFFECTS = ["frei0r-filter-scale0tilt"]
+
+HIDDEN_EFFECTS = [
+    # Overlaying an image onto a video stream can already be done.
+    "gdkpixbufoverlay",
+    "frei0r-filter-scale0tilt"]
 
 GlobalSettings.addConfigSection('effect-library')