On Python 3, cgi.FieldStorage has a __del__ method that closes the underlying file [1]. This means that if the copy made from UnicodeMultiDict._decode_value is garbage collected, the file underlying the original FieldStorage will be closed! Fix this by not copying FieldStorage if it is not required by decode_keys=False. I cannot think of a nice way to fix this problem if decode_keys=True.

[1] https://github.com/python/cpython/commit/f79126f373a9d5c9b584a8db736fe490fcbfa77a

This fixes a deprecation warning on 3.7.

Future is calling installation endless recursion. We are only
using it for an html.escape method, so we make our own and get
rid of future.

Related-Bug: #6

pytest exposes many warnings, some but not all of which are cleaned
up here. The main switch is to use html.escape instead of cgi.escape.
This inspired the addition of 'future' to requirements.

The remaining warnings are related to pytest deprecations or over-eager
test discovery.

It is perhaps ironic that the switch to pytest is to avoid nose being
mostly dead, and now we are using features in pytest that pytest wants
to make dead. These are left for later cleanups, which means that
running the tests is noisy.

See https://www.python.org/dev/peps/pep-0479/