Require py>=1.8.2 so we can rely on correct hash() of py.path.local n Windows

[bluetech]

See https://github.com/pytest-dev/py/blob/1.8.2/CHANGELOG#L4.
Fixes #7357.

[nicoddemus]

Thanks!

While at it, would you mind taking care of this comment?

pytest/setup.py

Lines 3 to 4 in b322004

	# TODO: if py gets upgrade to >=1.6,
	# remove _width_of_current_line in terminal.py

(We lost it by accident it seems when moving settings to setup.cfg)

[nicoddemus]

Also, I think it is worth adding a trivial CHANGELOG entry for this. 👍

[bluetech]

@nicoddemus I added a changelog entry. The setup.cfg comment is actually no longer relevant ever since we imported TerminalWriter into pytest.

[nicoddemus]

Ahh right, thanks! 👍