Take out a flaky part of WalletTest that isn't relevant anymore since even immediate auto-saves now run on a separate thread. The auto-saving is tested elsewhere anyway.
Experimental tweak to the definition of the numBroadcastPeers confidence field: now it actually does what the name implies.
Wallet: improve double spend handling.

Now connects all inputs of an overriding transaction, meaning balance is correct if a bit-tweaked but semantically identical transaction double spends its shadow (e.g. during key rotation on a cloned device).

Still does not recursively kill transactions however.

Resolves issue 439.
Added MnemonicCode, implements BIP-0039.
Payment channels: clear a static analysis thread safety warning.
Add Ken to the AUTHORS file.
Merge remote-tracking branch 'upstream/master'

Conflicts:
	core/src/test/java/com/google/digitalcoin/core/WalletTest.java