add "primaries" as a synonym for "masters" in named.conf

as "type primary" is preferred over "type master" now, it makes
sense to make "primaries" available as a synonym too.

added a correctness check to ensure "primaries" and "masters"
cannot both be used in the same zone.

(cherry picked from commit 16e14353b1)

bin/tests/system/ixfr/ns5/named.conf.in

@@ -37,12 +37,12 @@ view "primary" {
 	zone "test" IN {
 		type slave;
 		file "mytest.db";
-		masters { 10.53.0.3; };
+		primaries { 10.53.0.3; };
 	};
 	zone "sub.test" IN {
 		type slave;
 		file "subtest.db";
 		request-ixfr no;
-		masters { 10.53.0.3; };
+		primaries { 10.53.0.3; };
 	};
 };