t4116-apply-reverse.sh: use $TAR rather than tar

Signed-off-by: Brandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4116-apply-reverse.sh

@@ -48,12 +48,12 @@ test_expect_success 'apply in reverse' '
 
 test_expect_success 'setup separate repository lacking postimage' '
 
-	git tar-tree initial initial | tar xf - &&
+	git tar-tree initial initial | $TAR xf - &&
 	(
 		cd initial && git init && git add .
 	) &&
 
-	git tar-tree second second | tar xf - &&
+	git tar-tree second second | $TAR xf - &&
 	(
 		cd second && git init && git add .
 	)