Prerender

Added
- Added ability for cluster master to kill last known phantomjs pid for a worker if the worker dies (preventing orphaned phantomjs instances)
Changed
- Better terminating for cluster workers

Added
- Added NUM_SOFT_ITERATIONS to try to kill phantomjs and reclaim memory when no requests are in flight. This should be set to a low number (1-10) so that PhantomJS can be restarted often when it isn't doing anything else. NUM_ITERATIONS should still be set to something like 40-50 to make sure to force kill PhantomJS even if a request is in flight.
- Added clearing of memory cache to prevent PhantomJS from returning a 304
Changed
- Fixed issue where prerender-status-code set to `200` was causing the page to skip being cached
- Fixed an issue where we weren't using the correct pid when trying to force kill PhantomJS.
- Moved clearing of memory cache and local storage to before the page loads instead of after. This will prevent edge cases that could cause a 304.

Changed
- Fixed issue where S3HtmlCache was calling next() before finishing saving to the cache

Changed
- Fixed issue where we were calling `hasOwnProperty` on a `querystring` that no longer had Object on it's prototype chain

Changed
- Fixed issue where a webpage calling window.close would cause Prerender to be unable to shutdown PhantomJS properly

Changed
- S3 cache plugin was incorrectly saving non-200 status code responses to the cache