Treat %error-verbose as %define error_verbose.

This allows to pass -Derror_verbose on the command line.  Better yet, it
allows to pass -Derror_verbose=$(ERROR_VERBOSE), with ERROR_VERBOSE being
defined as false or true.

	* data/bison.m4 (b4_percent_define_if_define): Instead of relying
	on b4_percent_define_ifdef, for does not check the defined value,
	but only whether the symbol is defined, rely on
	b4_percent_define_flag_if, so that a value of "false" is processed
	as a false.
	If not defined, define the flag to "false".
	(b4_error_verbose_if): New.
	* data/glr.c, data/lalr1.cc, data/yacc.c: Use it instead of
	b4_error_verbose_flag.
	* src/getargs.h, src/getargs.c (error_verbose_flag): Remove.
	* src/output.c (prepare): Don't output it.
	* src/parse-gram.y (%error-verbose): Treat as %define error_verbose.

data/lalr1.cc

@@ -1,6 +1,6 @@
 # C++ skeleton for Bison
 
-# Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008
+# Copyright (C) 2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009
 # Free Software Foundation, Inc.
 
 # This program is free software: you can redistribute it and/or modify
@@ -116,7 +116,7 @@ m4_popdef([b4_dollar_dollar])dnl
 
 
 m4_pushdef([b4_copyright_years],
-           [2002, 2003, 2004, 2005, 2006, 2007, 2008])
+           [2002, 2003, 2004, 2005, 2006, 2007, 2008, 2009])
 
 m4_define([b4_parser_class_name],
           [b4_percent_define_get([[parser_class_name]])])
@@ -169,7 +169,7 @@ dnl FIXME: This is wrong, we want computed header guards.
 # undef YYERROR_VERBOSE
 # define YYERROR_VERBOSE 1
 #else
-# define YYERROR_VERBOSE ]b4_error_verbose_flag[
+# define YYERROR_VERBOSE ]b4_error_verbose_if([1], [0])[
 #endif
 
 /* Enabling the token table.  */