end-to-end testing for #167

[StefanKarpinski]

The tests added for #167 test the helper function content_length but don't do any kind of end-to-end testing that the new functionality works. The way to test would be to make a request to httpbingo that would have been chunked previously but is no longer chunked. However, I haven't figured out a way to tell if an upload request to httpbingo was chunked or not, which is necessary for that test.