net: type check createServer options object

net.createServer('aPipe') and net.createServer(8080) are mistakes,
and now throw a TypeError instead of silently being treated as an
object.

PR-URL: https://github.com/nodejs/node/pull/2904


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>