ioset event handling fixups

src/ioset.c (ioset_connect): Properly handle the situation if the connect
    handler closes the fd.
  (ioset_accept): Rename "old_active_fd" to "old_active" for consistency.
  (ioset_buffered_read): Make sure we bail if the fd is closed.
  (ioset_events): Handle 'readable' on a connecting fd as an error.
git-archimport-id: srvx@srvx.net--2006/srvx--devo--1.3--patch-49