[wsgi] avoid reading the entire request body in memory Import POST form handling code from https://raw.github.com/defnull/multipart/master/multipart.py to avoid reading arbitrary amounts of data from the network in memory. NOTES: - In the twisted case we limit the max request content-length to 100MB (by default), which seems kind of arbitrary, but avoids this issue - werkzeug.formparser has suitable code as well, but I don't know if we want to add it as a dependency