Fix misleading error message

This message is shown if fcntl() fails (for any reason)

	ioping: fcntl failed, please retry without -D: Invalid argument

First, it tells that -D is invalid argument, which is misleading.

Second it tells to retry with -D even if -D was not used.

Fix it, now the message is:

	ioping: fcntl failed: Invalid argument
	Please retry without -D
Signed-off-by: Kir Kolyshkin <kir@openvz.org>

ioping.c

@@ -380,8 +380,13 @@ int main (int argc, char **argv)
 			err(1, "failed to create temporary file at \"%s\"", path);
 		if (unlink(temp))
 			err(1, "unlink \"%s\" failed", temp);
-		if (fcntl(fd, F_SETFL, flags))
-			err(1, "fcntl failed, please retry without -D");
+		if (fcntl(fd, F_SETFL, flags)) {
+			warn("fcntl failed");
+			if (direct)
+				fprintf(stderr, "Please retry without -D\n");
+			exit(1);
+		}
+
 		for (woffset = 0 ; woffset + size <= wsize ; woffset += size) {
 			if (pwrite(fd, buf, size, offset + woffset) != size)
 				err(1, "write failed");