Fixed flask handler to actually accept and handle x-frpc content type.
Fixed flask handler to actually accept and handle x-frpc content type.

Due to the negotiation in all my previous test I didn't notice that the server didn't and couldn't accept binary data with x-frpc header. Fixed this to work with uWSGI, support for the rest of WSGI servers should be added eventually.

seznam/fastrpc,seznam/fastrpc,seznam/fastrpc,seznam/fastrpc,seznam/fastrpc,seznam/fastrpc