A verified unverified-consensus should be renamed to cached-consensus

If Tor with a fresh $DATA_DIR gets a consensus and cannot verify, Tor writes it as $DATA_DIR/unverified-consensus. If Tor then is restarted and suddenly can verify unverified-consensus for whatever reason, Tor will start using it and never write a cached-consensus. While this doesn't cause Tor to misbehave AFAICT, the name of unverified-consensus is misleading since it in fact isn't unverified any longer.

Steps to reproduce:

1. rm $DATA_DIR/*-consensus
2. date --set="Jan 1 00:00:00 UTC 2013" # or whenever all current authority certs are expired
3. start tor
4. verify that Tor is not working and that you got $DATA_DIR/unverified-consensus
5. stop tor
6. set correct system time
7. start tor
8. verify that Tor is working and that there's no $DATA_DIR/cached-consensus, only $DATA_DIR/unverified-consensus