@summary Returns the current async transaction for this container layer. A new transaction is created if one did not already exist. This method will always return an open, uncommitted transaction. @desc ck_isAsyncTransactionContainer does not need to be YES for this to return a transaction.

@summary Goes up the superlayer chain until it finds the first layer with ck_isAsyncTransactionContainer=YES (including the receiver) and returns it. Returns nil if no parent container is found.