fill-paragraph doesnt work, lp:1286318

ert test added
Unused variable `py-enforce-output-buffer-p' removed

The idea was to enforce value of `py-output-buffer' for output-buffer.

This might be done smarter with `py-output-buffer', which is used when set.

Changed the default to an empty string, which evaluates to nil.

Thus by default output arrives in py-shell buffer, commonly "*Python*".
py-ert-execute- tests rearranged
tests fixed

py-shell-invoking-python3-lp:835151-test
py-shell-invoking-python2-lp:835151-test
Some more tests fixed

execute-indented-code-lp:828314-test
py-execute-region-python2.7-switch-test
complaint-about-non-ASCII-character-lp-1042949-base
ipython-complete, lp:1284141

again

`py-docstring-p'

Assume inside a docstring if its start equals beginning
of statement