[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
I guess the rest of the tests use the `expected =...` notation, and I've never really run into a problem using it honestly.  I'll change it...