variables: parse.error

variables: parse.error

Implement, document, and test the replacement of %error-verbose
by %define parse.error "verbose".

	* data/bison.m4 (b4_error_verbose_if): Reimplement to track the
	values of the parse.error variable.
	Make "simple" its default value.
	Check the valid values.
	* src/parse-gram.y: Use %define parse.error.
	(PERCENT_ERROR_VERBOSE): New token.
	Support it.
	* src/scan-gram.l: Support %error-verbose.

	* doc/bison.texinfo (Decl Summary): Replace the documentation of
	%define error-verbose by that of %define parse.error.
	* NEWS: Document it.

	* tests/actions.at, tests/calc.at: Use parse.error instead of
	%error-verbose.