Python2.6 - Python3.3 support

I fixed code from <a href='https://github.com/django-debug-toolbar/django-debug-toolbar/issues/373'>graingert's pull request</a>. Now it works the same way as in original pypi package on python2.7 + Django1.5.1

Tested it manualy, and it works on Python 2.7.3, 3.2.3 and 3.3.1 version.

As we going to support Django 1.5, i assume we can drop python2.5 support. Just like Django1.5. So we can use futurestatements in code. It makes the code easier to adapt to new versions of python.

![djtb_portonpy3](https://f.cloud.github.com/assets/4037704/378207/79002f4a-a524-11e2-9810-819a2d146e17.PNG)

![djtb_portonpy3-sql](https://f.cloud.github.com/assets/4037704/378209/bf82151e-a524-11e2-9d2a-c83425c38ac9.PNG)