Fixes for runInTransaction

* always pass a value for json in makeReq so that request takes care of sending headers for json and parsing object from response body
* read the correct value for transaction id
* couple of typos and other minor fixes
This could be dangerous. Future commits will be done non-transactional, but the user doesn't have a well understanding of this fact. It may be much better to remove this line, or return with error before making the request if the transaction is already committed.