Fixed Python setup bug. Now the setup script works with Python version 2.6+
InternalTarget stores original dep. addresses

Useful for inspecting the dependency graph, which otherwise
throws away knowledge of JarLibrary and "dependencies" nodes

Also register "dependency_addresses" on JarLibraries
Add goals which find dep paths between two targets
Updated file following feedback from @jsirois.

1. PY variable handles the path to python.
Fixed one line that I left out by mistake: python -> $PY.
Merge pull request #129 from hwasungmars/master

Minor bugfix on Python version detection.
Merge pull request #130 from ryan-williams/paths

Add "path" and "paths" goals for finding dependency paths between targets
add default arg for context.py requested_goals
Merge pull request #132 from ryan-williams/default-arg-fix

add default arg for context.py requested_goals