correctly handle empty POST parameters

[kung-foo]

#585 only fixed empty GET parameters. This pull adds empty POST parameter support.

[dram]

Will this pull request be merged in?

[bdarnell]

Thanks for the reminder; I've just merged it.

[dram]

Thx.

It seems that some redundant code left after merge, namely:

---

     uri_arguments = parse_qs_bytes(native_str(body))
     for name, values in uri_arguments.items():
         values = [v for v in values if v] 

---

[bdarnell]

Thanks; fixed.