socket.fp has no readinto

[hackalog]

on python 2, socket.fp doesn't have a readinto() method, leading to errors like that seen here: kivy/kivy-ios#322 (comment).

Work around this limitation the same way it is worked around in read(); e.g.

python-future/src/future/backports/http/client.py

Lines 556 to 561 in a8114e4

	if PY2:
	data = self.fp.read(len(b))
	n = len(data)
	b[:n] = data
	else:
	n = self.fp.readinto(b)

[jmadler]

Thanks for doing this! Can you add a unit test for regression testing please?