* src/derives.c (print_derives): Be sure to use `>= 0', not `> 0',

* src/derives.c (print_derives): Be sure to use `>= 0', not `> 0',
when walking through ritem, even via rule->rhs.
* src/reduce.c (dump_grammar, useful_production, reduce_output)
(useful_production, useless_nonterminals): Likewise.
(reduce_grammar_tables): Likewise, plus update nritems.
* src/nullable.c (set_nullable): Likewise.
* src/lalr.c (build_relations): Likewise.
* tests/sets.at (Nullable): Adjust.
Fortunately, now, the $axiom is no longer nullable.