v1: uploads must set ContentLength on Request, not manually
v1: uploads must set ContentLength on Request, not manually

/cc @sethvargo - Well this was terrible to trackdown, including just
using `nc` as my HTTP server to see what we were sending.

If you don't set `ContentLength`, net/http just strips your other
manually set `Content-Length` header, and adds `Transfer-Encoding:
chunked`. Both of these things are not what binstore (or any file upload
server) expects. :|

hashicorp/atlas-go,hashicorp/atlas-go