Review implementation of decompressive transcoding

[coryan]

I am not sure the implementation of decompressive transcoding works as it should. It seems to decompress the data when uploaded:

storage-testbench/testbench/handle_gzip.py

Lines 29 to 34 in 465f85e

	def __call__(self, environ, start_response):
	request = Request(environ)
	if request.headers.get("Content-Encoding", "") == "gzip":
	request.data = gzip.decompress(request.data)
	request.environ["wsgi.input"] = io.BytesIO(request.data)
	return self.app(environ, start_response)

But that probably won't work with uploadType=multipart, where the Content-Type is multipart/related;. I think we need to decompress the results on the fly, and disable decompression if the Accept-Encoding: gzip flag is enabled. We also need to store the checksums of the compressed data, which suggests (again) that decompressing the request is not the right idea.