When you change gamedirs, cachepics (such as your conback) will be reloaded

in GL..  Please test this extensively, I _think_ the tempfile loader is
smart enough to handle what I'm doing properly.  If it's not, we'll have
to fix a slight memory leak.

source/draw.c

@@ -75,6 +75,16 @@ qpic_t	*Draw_PicFromWad (char *name)
 	return W_GetLumpName (name);
 }
 
+/*
+	Draw_ClearCache
+
+	This is a no-op in software targets
+*/
+void
+Draw_ClearCache (void)
+{
+}
+
 /*
 ================
 Draw_CachePic