When a device announcement is received for a known device at a new location, check whether the old location is still available before removing the old device and adding a new one.  See #637.
Tweak MdnsPlatform destruction to fix a possible timer deadlock.  See #810.
Assumption in test has been invalidated by a buggy Android renderer
Fix another test that was vulnerable to aVia strangeness
Fix for ref leaks when a device changes location.  See #637.