[Gm2] Exception handling, Python and Swig

[Gaius Mulley]

Hi,

I've just checked in a few more changes:

   * gm2/gm2-compiler/M2Swig.mod:  modified so that it
     produces a C++ style swig interface.  Also modified
     to include the language independent exception code.
   * gm2/examples/swig/full-strlib/Makefile:  modified
     swig command line to use C++ style interface.
   * gm2/examples/swig/strlib/Makefile:  modified
     swig command line to use C++ style interface.
   * gm2/examples/swig/tiny/Makefile:  modified
     swig command line to use C++ style interface.
   * gm2/examples/swig/exceptions:  new example which
     demonstrates Python catching a GNU Modula-2
     exception.

So swig now has to be used with the -c++ parameter if you wish to the
the gm2 automatic method of producing interfaces files via -fswig.
I've updated all the swig examples and also created a new screencast
showing that Python can catch GNU Modula-2 exceptions.

http://floppsie.comp.glam.ac.uk/download/screencasts/gnu-modula-2/python/python-exception-gnu-modula2.mp4

There are also some regression tests which test c++ throwing an
exception and GNU Modula-2 catching them and visa versa, maybe these
should also be in the examples directory?

regards,
Gaius