Changed local domain handling

 1. The local domain is now ".weave.local", which is safer from TLD
 pollution
 2. If the name given for an IP isn't a subdomain of the local domain,
 ignore it
Replaced ad-hoc printf with log levels
Replaced another log.Printf

(in a file I hadn't noticed)
Added logging.go, required by prior changes
Updated README re local domain
Merge remote-tracking branch 'upstream/master'
Adjust test to match change in ListenHttp
Set up defaults so it doesn't crash in tests