cocci: simplify "if (++u > 1)" to "if (u++)"

It is more common to use post-increment than pre-increment when the
side effect is the primary thing we want in our code and in C in
general (unlike C++).

Initializing a variable to 0, incrementing it every time we do
something, and checking if we have already done that thing to guard
the code to do that thing, is easier to understand when written

	if (u++)
		; /* we've done that! */
	else
		do_it(); /* just once. */

but if you try to use pre-increment, you end up with a less natural
looking

	if (++u > 1)

Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/coccinelle/preincr.cocci

@@ -0,0 +1,5 @@
+@ preincrement @
+identifier i;
+@@
+- ++i > 1
++ i++