[antlr-interest] Switching buildAST to true causes "InvalidASTnode type" error.

[Micheal J]

> Just tried the calc example and it works a treat. In
> my code COMMA has a token type of 6 in *TokenTypes.cs
> but the heteroList index trying to be retrieved for
> the attempted assignment to FactoryEntry in
> ASTFactory.cs is 7.

Weird. In any case there was an ASTFactory bug (related to that
Debug.Assert) that's now fixed. I'll post something tommorrow.

Micheal