As per https://peps.python.org/pep-0394/, the python binary can be one
of the following options:
- Python 2
- Python 3
- Not exist
All of the scripts in libxml2 use 'python', which may not exist.
As Python 2 reached EOL on the 1st January 2020, it's safe to move the
scripts to use python3 explicitly.
* tree.c: hardened the addChild function
* python/generator.py python/libxml.c python/libxml2-python-api.xml
python/libxml2class.txt python/libxml_wrap.h python/TODO:
added accessors needed for xmlNode, a bit more testing and
extension of interfaces
* python/tests/Makefile.am python/tests/build.py: added a test
build from scratch/save/load/check
Daniel