Avoid epoll_ctl(..., EPOLL_CTL_DEL, ...) for closed fds.

Avoid epoll_ctl(..., EPOLL_CTL_DEL, ...) for closed fds.

src/ioset-impl.h (struct io_engine): Add "os_closed" parameter to
    remove() method.

src/ioset.c (ioset_close): Add this to the call.

src/ioset-epoll.c (ioset_epoll_remove): Use it to avoid removing the fd
    from epoll_fd, since that epoll_ctl() call will always fail.

src/ioset-select.c (ioset_select_remove): Ignore the new parameter.
git-archimport-id: srvx@srvx.net--2006/srvx--devo--1.3--patch-81