2.5

Stablity commit: on render, all running jobs are stopped now (previews, 
composite, screencast). First render has to be more threadsafe, to allow
multiple renders simulatenously.

source/blender/editors/screen/screen_ops.c

@@ -2885,10 +2885,13 @@ static int screen_render_invoke(bContext *C, wmOperator *op, wmEvent *event)
 	RenderJob *rj;
 	Image *ima;
 	
-	/* only one job at a time */
+	/* only one render job at a time */
 	if(WM_jobs_test(CTX_wm_manager(C), scene))
 		return OPERATOR_CANCELLED;
 	
+	/* stop all running jobs, currently previews frustrate Render */
+	WM_jobs_stop_all(CTX_wm_manager(C));
+	
 	/* handle UI stuff */
 	WM_cursor_wait(1);