Turn python-environment--verbose into a public variable or defcustom?

[tkf]

It is useful when debugging.
See: tkf/emacs-jedi#148

[syohex]

I agree.

Should we rename python-environment--verbose to python-environment-verbose
if it is public variable ? Double dash means private/internal functions or variables.

[tkf]

Yes, we should change double dash to single dash. And mark the double dash as an obsolete alias.