optional package to register python in Windows registry

[maphew]

It can be helpful sometimes to register the gdal version of python with Windows. This way a) .py files can be run from outside the o4w shell, and b) 3rd party python programs which aren't part of the o4w package system can be installed using traditional python installers and eggs.

Here is a how to for (de)registering a given python install: ​http://effbot.org/zone/python-register.htm

As there can only be a single major version registered at a time, e.g. only one python 2.5, we would need to add logic to skip if one is already there.