Implement consistent cross-platform random number generation

```
ForPlay.random() is far too simplistic, and isn't even consistent across 
platforms.

See the discussion here for better ideas:
  https://groups.google.com/d/topic/gwt-forplay/PxQ6kI-BN8w/discussion
```

Original issue reported on code.google.com by `jgw@google.com` on 11 Jun 2011 at 1:35
