variables: prefer error-verbose to error_verbose.

variables: prefer error-verbose to error_verbose.

	* data/bison.m4 (b4_error_verbose_if): Based on error-verbose
	instead of error_verbose.
	* src/scan-gram.l (%error-verbose): Map the error-verbose
	variable.
	* doc/bison.texinfo: Promote %define error-verbose instead of
	%error-verbose.
	* tests/actions.at: Prefer %define error-verbose to %error-verbose.