jnb/synapse — pull request #1 by jnb (2014-09-30 20:59:48+00:00)
Title: Add 'use_previous_backends' option.

* This option defaults to true: if there are no default servers and a watcher
reports no backends, then use the previous backends that we already know
about.
* Factor out code that updates '@backends' into the watcher base class.