Wallet throws on missing signature by default

Using dummy sigs by default may be confusing for multi-sig scenarios.
See: https://groups.google.com/forum/#!topic/bitcoinj/PEhZGk3WMxU
Fix version message. My heart breaks when I see the bad spelling of our dearest child in the logs.
Don't bother pointless attempt to construct thread pool with no open circuits.
WalletTest: Better unit test failure message to check if the test is flaky.
Provide a more meaningful exception when reaching past end of ASN.1 stream. Properly close ASN.1 decoder in exception paths.

A way to trigger the exception is running ScriptTest.dataDrivenValidTransactions().
Update script JSON tests from upstream.
Introduce textual checkpoint format. It's basically one base64-encoded line per checkpoint.

The BuildCheckpoints tool now generates and sanity checks both formats.