[FINAL] Validating hash when downloading/extracting bundles.

An attempt to validate bundle hashes as they come in the door.  I was able to sha1 hash the file contents as they stream in, avoiding secondary passes over the file contents.

This is a follow on attempt to #32
Why is this? This `downloadFile` was meant to be generic, agnostic of any bundle or anything, simply to download **any** file.