added maximum depth command-line argument (-d) and scene option (max_depth); prettified elapsed time output when greater than 60 seconds

git-svn-id: svn://anubis/fart/trunk@203 7f9b0f55-74a9-4bce-be96-3c2cd072584d

scenes/infinity.fart

@@ -3,9 +3,10 @@ scene
 {
     options
     {
-        multisample 3
+        multisample 4
         width 1024
         height 768
+        max_depth 15
     }
 
     camera