Format code and check with 2to3 for src/core

graphSearch.py

src/core/distance.py

src/core/dryvrcore.py

src/core/dryvrmain.py

src/core/goalchecker.py

src/core/graph.py

src/core/guard.py

src/core/initialset.py

src/core/initialsetstack.py

src/core/reachtube.py

src/core/reset.py

src/core/uniformchecker.py