show postData in onResourceRequested callback (issue 158)

Someone offered make proxy here http://code.google.com/p/phantomjs/issues/detail?id=158
But I don't see reason why why my solution will not work

May be `std::numeric_limits < qint64 >::max()` is not best way, but outgoingData->size() return always 0. here is discussion of same problem http://stackoverflow.com/questions/5450551/qnetworkaccessmanager-read-outgoingdata-and-keep-it-in-qiodevice

Do you think its fine or there is a better way to do it?