ev_reader and ev_writer now own the FDs you give them. This is

helpful because they are in a better position to know when to close
them.  They can be tied together to share one FD between the two.

It is still (currently) necessary to explicitly cancel a reader if the
corresponding writer fails.  This may be changed in the future.

Hopefuly this should make event loop bugs at least more tractable.

Currently there is still lots of logging cruft.  This should be
removed before release.