Clarify position of open brace in multiline conditionals

[warsaw]

From https://mail.python.org/pipermail/python-dev/2017-June/148223.html

But the latter example continuation lines are intended at the same level as the following block of code. I propose to make exception for that case and allow moving an open brace to the start of the next line.

I agree with Serhiy; pull request coming momentarily.