bug#24809: 25.1; Python.el improper indention after backslash-assignment-continuation

[npostavs]

Jules Tamagnan <jtamagnan@gmail.com> writes:

> The bug is quite simple.
>   - Open a python file.
>   - Type:
>     hello = \
>   - C-m ; newline
>
> The point will now be directly under the backslash character. This is
> indented incorrectly according to the pep8 style guide and the
> pycodestyle checker, it should instead be indented
> `python-indent-offset` further than the previous line.

So the patch works (additionally the python-indent-after-backslash-4
test would need to be updated) but I'm not sure if it's correct.
Currently, the pep8 style guide doesn't really say anything about
indentation following backslash, it just recommends using parens
instead.