Support >2GB payloads in a single request when running default http driver on Java 7

The default http driver uses java's HttpUrlConnection, which uses an integer to determine fixed length of content. This means that it cannot be used to send >2GB content. The current workaround is to use an http driver that supports >2GB payloads in a single request.

This issue will conditionally allow the default driver to support >2GB payloads in a single request. It will do so via conditionally using setFixedLengthStreamingMode(long) on Java 7 and setFixedLengthStreamingMode(int) on Java 6:

https://gist.github.com/andrewgaul/6439757