Don't include local line on platforms without support

Since we now include a sample line for replication on local
connections in pg_hba.conf, don't include it where local
connections aren't available (such as on win32).

Also make sure we use authmethodlocal and not authmethod on
the sample line.

src/backend/libpq/pg_hba.conf.sample

@@ -84,6 +84,6 @@ host    all             all             127.0.0.1/32            @authmethod@
 host    all             all             ::1/128                 @authmethod@
 # Allow replication connections from localhost, by a user with the
 # replication privilege.
-#local   replication     @default_username@                                @authmethod@
+@remove-line-for-nolocal@#local   replication     @default_username@                                @authmethodlocal@
 #host    replication     @default_username@        127.0.0.1/32            @authmethod@
 #host    replication     @default_username@        ::1/128                 @authmethod@