PeerGroup: bugfixes to backoff.

1) Do the wait even on the exception path so if discoverPeers throws, we don't bypass the sleep.
2) Move some field accesses inside the lock.

Resolves issue 527.
WalletTool: automatically use localhost in regtest mode.
PeerGroup: tweak global backoff to be faster.
Consistently mark parent as nullable in TransactionOutput
More mock clock conversions, to avoid failures when running test cases independently.

Probably we should be injecting a mock Clock class so it goes away at the end of each test, but this would complicate the API somewhat.
Fix unit test broken by less aggressive backoff time.
Cheap test to see if an input stream is a wallet.
Extract getDisplayNameFromCertificate() into new X509Utils class. Also joins PkiVerificationData.name and .orgName into one .displayName. Adds tests using client/smime certificates of mine.
Extract loading of X.509 trust stores to TrustStoreLoader.