syscall: add some debugging to TestGetfsstat

TestGetfsstat is failing on OS X 10.8.

Not sure why. Add more debug info.

Change-Id: I7dabb70dd7aeffda7e8959103db9e4886b84741e
Reviewed-on: https://go-review.googlesource.com/28220Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/syscall/syscall_bsd_test.go

@@ -18,6 +18,7 @@ func TestGetfsstat(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
+	t.Logf("num fs = %v", n)
 
 	data := make([]syscall.Statfs_t, n)
 	n, err = syscall.Getfsstat(data, MNT_WAIT)
@@ -26,9 +27,9 @@ func TestGetfsstat(t *testing.T) {
 	}
 
 	empty := syscall.Statfs_t{}
-	for _, stat := range data {
+	for i, stat := range data {
 		if stat == empty {
-			t.Fatal("an empty Statfs_t struct was returned")
+			t.Errorf("index %v is an empty Statfs_t struct", i)
 		}
 	}
 }