Swig-friendly distutils.command.build_ext

[George Sakkis]

I'm using a custom extension of the build_ext distutils 'command' that integrates better with SWIG.
Specifically, it:

1. Adds '-I' (include) swig option for each directory containing a source file in the given
Extension.
2. Determines whether to add the '-c++" option by checking the source file extensions (even if the
'swig_cpp' and 'swig_opts' do not explicitly specify that it is a c++ wrapper).
3. Builds the swig-generated high-level python module (currently only the low level .dll/.so is
built).

If these changes are generally useful, I think they (c|sh)ould make it into the next release of
distutils.

George