[portland] How to tell an application python3 is installed

[Rich Shepard]

   The TreeLine tool I use has a new version that requires Python3 > 3.2. I
have both -2.7.5 and -3.3.3 installed. But, when I invoke 'python
install.py' the error message displays that python3 is required. How do I
specify that there is an appropriate version installed?

Rich