Differentiate between manual throw and natural gas exhaustion

[rphmeier]

In the light client, when executing eth_call or eth_estimateGas, we start with a small amount of gas and double it each time the result is exceptional, until the block gas limit is reached. Being able to differentiate between the request actually running out of gas and a deliberate throw would let us avoid making many redundant requests.

[rphmeier]

I think this is already handled but we don't have a test for it. We should just try the rpc::light_helpers::execute_tx with a proof of some call that throws. Probably easier said than done -- setting up the contract, state, and state proof necessary for that will probably be a nuisance.

[folsen]

@tomaka Anything you'd be interested in picking up?

[tomaka]

I can pick this up in the next few weeks.