[Python.NET] Python 2.5 compatibility and interop.cs

[Christian Heimes]

For your information:

I've created an EXPERIMENTAL branch:
https://pythonnet.svn.sourceforge.net/svnroot/pythonnet/branches/clr-2.0-python-2.5-branch/
It is NOT ready for production! Overloading and exception are currently
broken but I'm working on it.

I've also added project files and a solution file for MS VC#. The files
are also working with the free Express Edition.

Christian