Reformat log messages in DnsDiscovery and add one log message for the success case, to make more clear what's going on.

Also, rename hostNames to dnsSeeds as this name is more speaking for itself, and is used in other places as well.
Correctness fix: compare nBits directly not in BigInteger form as nBits has multiple non-canonical encodings.
Refresh wallet-template checkpoints file.
BuildCheckpoints: compare strings correctly.
Wallet: keep risk dropped txns around in RAM and don't miss them when a Bloom filtered block includes them. Resolves issue 545.
Don't crash if there's no logging handler installed.
Upgrade scrypt library.