mkfiles: check for test/mkfile when recursing

Some programs have test directories without a test
mkfile; this causes spurious errors. Discriminate
more carefully.

sys/src/cmd/mkmany

@@ -82,7 +82,7 @@ clean:V:
 man:V:	$MANFILES
 
 test:VQ: $PROGS
-	if(test -d ./test)
+	if(test -f ./test/mkfile)
 		cd test && mk $MKFLAGS test
 	if not
 		status=()

sys/src/cmd/mkone

@@ -63,7 +63,7 @@ $MAN/%:    %.man
 man:V:    $MAN/$TARG
 
 test:QV: $O.out $TESTDEP
-	if(test -d ./test){
+	if(test -f ./test/mkfile){
 		pwd
 		@{cd ./test && mk $MKFLAGS test}
 	}