[Bug-gnubg] multiply evaluation code comments

[David Montgomery]

Hi,

At GamesGrid we're about to put up a 2-ply bot.
In reviewing some of the settings I concluded
that some comments in eval.h were misleading.

Please correct me if I'm wrong.

For movefilter a comment says "always allow this 
many moves. 0 means don't use this level, since 
at least 1 is needed when used."  Maybe 0 still 
implies to not use this level, but I see that
the default filter uses -1 and FindnSaveBestMoves
tests < 0, not <= 0.  

In fact, looking at the default filter I'm not 
sure what 0 means for Accept.  0 is used for the 
even ply, and -1 for the odd ply.  To be honest,
I don't know why Accept isn't always -1 on the
diagonal, since once you've evaluated at the
max ply we are going to, there's no need to filter.

For evalcontext a comment says about nReduced:
"this will need to be expanded if we add support 
for nReduced != 3".  In fact, nReduced 2, 3, and
4 (and 0) all appear to be supported, and up to
7 could fit in the bitfield.

David