Add additional signing + hashing api tests.
Add additional signing + hashing api tests.

ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-tx,ethereumjs/ethereumjs-vm,ethereumjs/ethereumjs-tx,ethereumjs/ethereumjs-vm,ethereum/ethereumjs-vm,ethereum/ethereumjs-tx