* src/symlist.h, src/symlist.c (symbol_list_length): New.

* src/scan-gram.l (handle_dollar, handle_at): Compute the
rule_length only when needed.
* src/output.c (actions_output, token_definitions_output): Output
the full M4 block.
* src/symtab.c: Don't access directly to the symbol tag, use
symbol_tag_get.
* src/parse-gram.y: Use symbol_list_free.