req/rep example uses push/pull socket types

[rgrinberg]

typo?

[andrewstarks]

Not sure if this is related, but the example script causes a segfault on the Mac. Right now, I'm just making the examples run and not actually debugging them, I it might be obvious using push/pull would cause this issue. I just wouldn't know that. :)

[TTimo]

aren't lines like: assert (nn_bind (sock, url) >= 0); no-ops at compile time? e.g. the nn_bind will never run

[spot62]

Wrong code in Request/Reply example part of original article