PYTHON_HOME and Windows paths

[Keegan Witt <keeganwitt gmail com>]

I'm not sure if anyone besides me is using the feature that lets you use your existing Python installation rather than using a separate Python instance.  I'm thinking of introducing a breaking change: instead of making users point PYTHON_HOME to a Python installation that is compatible with Meld, I'm thinking of using a separate environment variable (like MELD_PYTHON) they can use to pick between however many Python installations they have.

If we go that route, I'm thinking to add a page to the installer that lets you copy your existing PYTHON_HOME to this new variable, and also lets you export the Meld path to your path (both would be unchecked by default to work with the existing defaults).

What do you think?

-Keegan