Create Match variale "_M" for each MatchRule.

It would create one only if top-level parse_match_operator
parser rule had been used. Now it creates it within
match_rule_operator parser rule, so it works for parse_wccl_file
as well.

libwccl/parser/grammar.g

@@ -282,7 +282,6 @@ parse_match_rule
 {
 	Lexicons empty_lex;
 	ParsingScope scope(tagset, empty_lex);
-	scope.variables().get_put<Match>("_M");
 }
 	: ret_match = match_rule_operator[scope] 
 ;
@@ -2325,6 +2324,7 @@ match_rule_operator
 	returns [boost::shared_ptr<MatchRule> ret_op]
 {
 	boost::shared_ptr<ApplyOperator> apply;
+	scope.variables().get_put<Match>("_M");
 }
 	: apply = match_apply_operator [scope] {
 		ret_op = boost::make_shared<MatchRule>(scope.variables(), apply);