Fix race of mock clock with current time if tests are all run sequentially. This commit requires you to use one of the setMockClock() variants before being able to roll it.
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.
PeerGroup: tweak global backoff to be faster.
Fix unit test broken by less aggressive backoff time.
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.
Cheap test to see if an input stream is a wallet.
TransactionInput: verify(): don't crash if the given output has no parent. Clears a static analysis warning.
Adjust MIN_NONDUST_OUTPUT down to 546 only for risk analysis. This is required because we start seeing more and more transactions using the new fee rules introduced with Bitcoin Core 0.9.

Conflicts:
	core/src/main/java/com/google/bitcoin/wallet/DefaultRiskAnalysis.java