Corrected call function in FakeExtVM

Vitalik found some discrepancies between the results of the vm tests of pyethereum and cpp-ethereum. This fix of the call function in FakeExtVM  corrects that.
I also had to add a new function to the state class in order to create contracts with given addresses. 
This mechanism was just copied and paste form the current create. And is now replaced by the function parameter _newAddress. this gives the possibility to create a new contract with a given address.