Update issue #291 : Don't call SetDefaultSyncSource on new graphs.

Clock selection behaviour now corresponds with GraphEdit.
When graph is first created use clock is off and a clock is automatically chosen when playback starts.
It seems that this 'auto-clock' state can't be recreated once a clock has been explicitly chosen except by creating a new graph.
The old behaviour can be recreated by explicitly selecting 'use clock' on a new graph which will call SetDefaultSyncSource.

src/display_graph.cpp

@@ -270,7 +270,10 @@ GRAPHSTUDIO_NAMESPACE_START			// cf stdafx.h for explanation
 
             AddToRot();
 
-			gb->SetDefaultSyncSource();
+			// Historically, GraphStudio and GraphStudioNext used to always call SetDefaultSyncSource on startup
+			// This has been removed as appears it's not DirectShow best practice cf issue #291
+			// gb->SetDefaultSyncSource();
+			// This behaviour can be simulated by turning the graph clock off and on again
 
 			gb->QueryInterface(IID_IMediaControl, (void**)&mc);