Resolve some XXXX012 items:
   - Remove PathlenCoinWeight: if we want it again, we can add it
     back in.
   - Ditto with RelayBandwidth*.
   - Decide to leave in the "hey, you didn't set end_reason!" BUG log message,
     but stop telling people to bug me personally.
   - Postpone strengthening assert_connection_ok(): it's important, but 
     it's also a good way to introduce weird bugs.
   - Move some expensive consistency checking from dns_free_all() into
     assert_cache_ok().


svn:r9533