client: another stupid style-mangling commit
client: respect content-length header and always set polling timeout

Fixes hangs on connections that don't get closed, but have no more
response data left.
Client didn't hang in the past, so maybe modern twisted keeps TLS
connections open after requests and older one didn't.
server: add twsted-logging observer
server.NotaryResponse: add Content-Length header
client.http: simplify content-length header regexp
client: fix display of cached fingerprint dates