[Bug-gnubg] Error rate of predefined settings

[Philippe Michel]

A few months ago, Timothy Chow asked about the weaker predefined
settings :

> approximately what Snowie error rate do these settings translate into? 
> Has anyone tested this out?

Sessions of about 500 games (money play without beavers) analyzed at 2 ply 
give :

expert           1.7
advanced	 7 
intermediate	24
casual          31
beginner        38

2 ply is not perfect, so the expert error rate is more likely to be about 
3 and the other may be slightly higher as well.

All in all, it looks like expert is in fact world class and advanced more 
or less what one would expect.

For the weakest levels, the mere definition of how an intermediate, 
casual or beginner is supposed to play is not obvious, but the way the 
error rates are spread out feels somewhow inadequate.