[core] check if SOCK_NONBLOCK is ignored (fixes #2883)
[core] check if SOCK_NONBLOCK is ignored (fixes #2883)

x-ref:
  "fdevent_init should check if SOCK_NONBLOCK works"
  https://redmine.lighttpd.net/issues/2883

gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,lighttpd/lighttpd1.4,gstrauss/lighttpd1.4,gstrauss/lighttpd1.4