Now Works with Python 2 & 3, Qt 4 & 5.

CMake now generates different librariy files depending on the linked Qt/Python versions:
PythonQt    - Qt 4.x + Python 2.x
PythonQt_3  - Qt 4.x + Python 3.x
PythonQt5   - Qt 5.x + Python 2.x
PythonQt5_3 - Qt 5.x + Python 3.x

Fix Qt 4 build.