Reimplement --securerandom

Seeds should be reproducable without the flag passed, and unreproducable with the flag passed.
With --securerandom, generate a 9-char alphanumeric string to use to make filenames differ.

PotShuffle.py

@@ -275,7 +275,7 @@ vanilla_pots = {
 
 
 def shuffle_pots(world, player):
-    import random
+    import RaceRandom as random
 
     new_pot_contents = {}