Add OwnershipTransferred event to Ownable contract and its derivatives#424

Merged

frangio merged 4 commits intoOpenZeppelin:masterfrom

eugene-babichenko:transfer-ownership-event

Sep 7, 2017

Commits on Sep 5, 2017

fire OwnershipTransferred event when the owner of an Ownable contract instance actually changed
eugene-babichenko
committed

Commits on Sep 6, 2017

Commits on Sep 7, 2017

fixed wrong call order in Ownable.transferOwnership
eugene-babichenko
committed