Vagrantfile to provide portable development environment

The Vagrantfile uses the script vagrant.sh to provision a Debian Linux
system to run PyExZ3. It could be tweaked to configure just about any
Linux system.

The .vagrant folder has been added to .gitignore as well.

Additionally I added `tmp.txt` to the ignore file as it is the output of
one of the test cases. Perhaps the tests would be better run inside of a
sandbox.
Working Vagrant Shell Provisioner

Needed the gettext package to compile git. I tried to use git 1.9 from
Wheezy backports, but it wasn't new enough for CodePlex.

Additionally removed the last command that ran the failing test cases.
Work-in-Progress Vagrant Documentation in the README
Updated README with Vagrant Instructions
Added VirtualBox Installation to Vagrant Instructions
Merge pull request #8 from GroundPound/vagrant

Vagrant-based Development Environment