Now that Python has been renamed it's important that we still output
which Python they are using for debugging purposes e.g.
```
Python: /usr/local/opt/python/libexec/bin/python => /usr/local/Cellar/python/2.7.13_1/Frameworks/Python.framework/Versions/2.7/bin/python2.7
```
Not quite a mass replacement as I've used OS X and Mac OS X where
describing specific older versions and added compatibility methods
for things in the DSL.
Due to our SCM wrapper in `Library/ENV/scm/git`, lookup is a bit more
complicated than just picking the first match in `PATH`. Make debugging
easier by printing the version and path of the Git actually used by us.
