netsock_server close listening socket after accept_loop exits.
Merge pull request #68 from chipdude/chip/misc

A motley collection
fix duplicate errstr() in http_error exception
set errno to correct value after epoll-reported socket error
use shutdown() to effect controlled stop of netsock_server
as libten uses fcntl, its third parameter is int, not long
formatting consistency with rest of class
provide convenience form of socket_fd::getsockopt, now matching setsockopt