Fix slideshow effects disappearing.

Fixes #316

data/blacklisted_effects.txt

@@ -15,7 +15,7 @@ frei0r.perspective
 #Effects not usable with a simple GUI
 #ladspa
 jackrack
-luma
+#luma
 data_show
 gtkrescale
 watermark

data/effects/CMakeLists.txt

@@ -20,6 +20,7 @@ grain.xml
 greyscale.xml
 invert.xml
 loudness.xml
+luma.xml
 mirror.xml
 mute.xml
 normalise.xml

data/effects/luma.xml

+<!DOCTYPE kpartgui>
+<effect tag="luma" id="luma" type="hidden">
+</effect>
+

src/doc/documentchecker.cpp

@@ -375,6 +375,9 @@ bool DocumentChecker::hasErrorInClips()
     for (int i = 0; i < max; ++i) {
         QDomElement transition = effs.at(i).toElement();
         QString service = getProperty(transition, QStringLiteral("kdenlive_id"));
+        if (service.isEmpty()) {
+            service = getProperty(transition, QStringLiteral("mlt_service"));
+        }
         filters << service;
     }
     QStringList processed;