clone the response

[laszlokorte]

Currently if multiple subscribers subscribe to one http request all get the same response object.
Now if multiple subscribers (or somewhere in the chain) call response.json() (or other reading methods) an exception is throws because json() (and other methods) are only allowed be called just once on each response.

I propose that the original response object should be shareReplay()'ed by the driver and then cloned for each subscriber.