Issue 586 fixed, 0BTC transaction with OP_RETURN will work.
Fix question marks could not be used in payment protocol request URI. Removes the check for multiple question marks in the bitcoin URI.

Also see https://github.com/schildbach/bitcoin-wallet/issues/169
WalletTool: magic --output value ALL for easier emptying of wallets.
When reading wallets, catch another possible data inconsistency and throw UnreadableWalletException.
PeerGroup: add a removePeerFilterProvider to complement add.
Delete EncryptedPrivateKey, it's cruft left over from the HD wallets work.
Wallet: give up on using read/write locks for the keychain, the re-entrancy rules are too hard to follow. Switch back to a regular lock.