Download File Attachments as tarball:

- only working with files stored on host filesystem and Amazon S3.

- now compresses into .tar.gz file instead.

- properly streams compressed file back to client.

- Download Attachments and Download Diff now under Downloads

  menu dropdown in review request editor.
- URL changed from: r/<requestID>/file/zip/ -> r/<requestID>/file/tar/

Tested on:

- Linux Mint 17: Chromium 37.0.2062.120

- Linux Mint 17: Firefox 32.0.3

- Windows 8.1: Chrome 38.0.2125.101

- Windows 8.1: Firefox 32.0.3

- Windows 8.1: Internet Explorer 11

Tested also with curl to see if file is streaming as expected.
Review requests with small files, large files (2mb+), and mix of both, tested and working with host file system and Amazon S3 storage option.