TempURL filename options; bug fixes

- Prior to this commit, a Content-Disposition header was always set
  on responses to GET requests, with the filename based on the object
  name. Now, the header will only be set for 2xx responses and the
  filename can be overridden with a filename query parameter on the
  request.

- Fixed a bug where all query parameters on the request were being
  passed down the WSGI pipeline. Now, just the query parameters
  useful in log-based debugging are included. This becomes important
  with things like the Bulk middleware that act upon query
  parameters.

- Fixed bug where the Content-Disposition header wasn't following RFC
  spec.

DocImpact

Change-Id: I66ad809321dcdd03444324973c8b76869e3b0c8e
Merge "TempURL filename options; bug fixes"