This class represents a model for a grammar. The content of the grammar includes the
definitions, start symbol, associativities and priorities.
author: Stephan Michels version: CVS $Id: ExtendedGrammar.java,v 1.19 2004/01/08 11:30:52 benedikta Exp $
Returns all definition for given nonterminal symbol as a list of indices.
Parameters: ntsymbol - Nonterminal symbol List of indices from the definitions