Fix response for mining.

USD-based pricing of gas.

Parity can accept older work packages

Caching for computing seed hashes (#541)

Code review changes

`ClosedBlock`s still keep the pre-finalised state (i.e. state after the last transaction).
`LockedBlock`s do not. New mining algo needs to reopen these `ClosedBlock`s, however enactment
system does not (and `ClosedBlock`s are slower & more hungry), hence the distinction.

checking transaction queue for pending transaction

refactored loading of state tests

tests for deserialization of transaction from issue #835

unlocks with no expiration [on top of 833]

Unlock accounts on CLI.

Make BlockNumber optional, fix eth_call

Test socket to common test code (ethcore-devtools)