Merge pull request #180 from dcousens/eckey1

ECKey WIF only
Merge pull request #181 from dcousens/mesnet

Message signing and altcoins
Merge pull request #182 from dcousens/ectests

EC Tests and further use of Buffers
Merge pull request #183 from dcousens/ecconst

EC constants and bitShifts
ecdsa: use shamirs trick
ecdsa: consistent parameter ordering
ecdsa: use (r, s) values directly
ecdsa: remove ECKey dependency in tests
ecdsa: remove implicit ecparams
ecdsa: use standard declarative notation for functions
ecdsa: fix indentation
sec: use a hashtable for lookup
sec: use BigInteger.fromHex directly
sec: fix formatting
bigi: upgrade to 1.1.0
ECKey: remove unnecessary slice
tests: remove bigi test fixture
tests: use JSON fixtures exclusively
message: data-driven tests
Wallet: cleanup createTx control flow

Unknowingly this also revealed a subtle bug in the previous
implementation which allowed the creation of transactions even
when no UTXOs existed.  This has been amended in the tests.