Added tests

Added tests for django tests for 1.4, 1.5 and 1.6. These are the tests from the django test dir for each version. These tests take quite a long time to run.  30 mins or so

to run:
```
python tests\runtests.py --settings=test_django_pyodbc
```
Current output for django 1.4 (testcases fail to run for django 1.6):

```
Ran 1325 tests in 9599.771s

FAILED (failures=106, errors=454, skipped=89, expected failures=1)
```
Based on the django version installed it will import the right tests. I am now working on getting it to run for django 1.6.