Request for code review - python exceptions mapped to C++ exceptions

[Barry S. <ba...@ba...>]

If any of you have the time to look over the latest changes to PyCXX I would
appreciate any feedback.

I have added code to pycxx that allows exceptions raise in Python to be caught 
in C++ using the Python exception name.

For example:

	try
	{
		call-python
	}
	catch( ValueError &e )
	{
		// handle value error
	}
	catch( UserDefinedError &e )
	{
		// handle user defined error
	}

See Demon/Python3/simple.cxx and simple.py for example code.

I have checked in the first pas of this code for python3 on trunk.
(I also created a pycxx-6.2-maint branch)

The way this works is to have a std::map (cxx_exceptions.cxx) that
contains a map from python type objects to a function that will raise the
C++ equivalent.

The fucntion ifPyErrorThrowCxxException is called everywhere pycxx code
is entered from python and an exception may have be raise. It will convert
into a C++ exception and throw it.

I think the code of SimpleError in simple.cxx is all boiler plate and I can
turn that into a macros. One to declare the other to init.

Barry