Make the setup.py runnable by Python 3 and run 2to3 automatically.

Conflicts:
	sandbox/run_2to3.sh
	setup.py
setup.py: exit after it has called itself.
setup.py: Fix bug if setup is not in the current working directory.
Fix previous commit
setup.py: Hide 2to3's output.
setup.py: Add the --debug switch.
setup.py: In debug mode, display 2to3 logs.
2to3/run.py: Fix compatibility issue with old Python 3.x versions (2to3 does not suport -W and -o).
Fix previous commit.
Fix typo.
Speed up install on Python3 (2to3 is ran only on modified files).
setup.py: Remove error output if not in a git repo.