variables: accept dashes.

variables: accept dashes.

	* src/scan-gram.l ({id}): Also accept dashes after the initial
	letter.
	({directive}): Use {id}.
	* src/parse-gram.y: Comment and formatting changes.
	* doc/bison.texinfo (Symbols): Adjust the lexical definitions of
	symbols.
	* src/complain.h, src/complain.c (yacc_at): New.
	* src/symtab.c (symbol_new): Use yacc_at to report inappropriate
	symbol names.
	* src/output.c (token_definitions_output): Do not #define token
	names with dashes.
(cherry picked from commit 4f646c3794c45940aaf96d5409eff02a2c74978e)

Conflicts:

	data/bison.m4
	src/parse-gram.y