Taking a long time for executing estimate_gas of tx with infinite loop.

[miyao-gmo]

When estimate_gas of tx with infinite loop was executed, RPC server returns no response for a long time.
In a following environment, it takes about 3 minutes for estimate_gas.

parity: v1.8.2
OS: ubuntu 16.04.1
Memory: 3G

contract A {
  function loop() {
    while (true) {}
  }
}

> var calcInfiniteLoopTime = function() {
... var start = new Date().getTime();
... A.loop.estimateGas(function(err, gas) {
..... var end = new Date().getTime();
..... console.log(end - start);
..... });
... }
> calcInfiniteLoopTime();
> 170040

Tx with 1,000,000,000,000 gas was executed (https://github.com/paritytech/parity/blob/master/ethcore/src/client/client.rs#L1234), so it takes a long time.
A parity node owner should decide whether estimate_gas upper limit is a block gas limit or UPPER_CEILING(1,000,000,000,000) by config.
If I skipped estimate_gas execution with 1,000,000,000,000 gas, it takes about 80 msec.