PyUnicode_AsEncodedString() instead of calling the encode() method of the
host, to handle correctly custom string with an encode() method which doesn't
return a byte string. The encoder of the IDNA codec is now called directly
instead of calling the encode() method of the string.

Patch from Shiyao Ma.

Patch by Elvis Pranskevichus.

Initial patch by Larry Hastings.

Patch by Elvis Pranskevichus