Add API call to sign a hash with an account key

New API call can specify a SHA256 hash and an account name, and the
wallet will sign the hash with the named account's private key and
return the signature. This is helpful for the URL login protocol.
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Wallet test for wallet_create_from_json and some blockchain* commands test
Hack around the resource leak by immediately closing the p2p tcp socket as soon as we get an exception during connection.
blockchain support for negative votes on next version bump
blockchain_list_block_test
Include genesis claims as virtual transactions in transaction history
Fix account name conflict detection
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Add compiler warnings for next hardfork
Alter wallet_sign_hash to return compact_signature instead of signature
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Merge branch 'master' of github.com:BitShares/bitshares_toolkit
Fix most regression tests

Failing:
blockchain_get_pending_transactions_test
blockchain_list_block_test