Gracefully handle EMFILE

Implementing a tip from Marc Lehmann:
http://pod.tst.eu/http://cvs.schmorp.de/libev/ev.pod#The_special_problem_of_accept_ing_wh

Keep an extra FD around for every server. When you hit EMFILE, destroy that
FD, accept a connection, close it; in this way you can clear the connection
queue and let people know that you're overload.

No more timeout needed.