_AM_PYTHON_INTERPRETER_LIST is used by AM_PYTHON_PATH to autodetect
Python programs whose names correspond to a specific Python
version (e.g. python3.6). Previously this list was updated manually.
The automatic support of newer versions (up to 4.0 excluded) fixes
bug#28160.
* m4/python.m4 (am_py_min_ver, am_py_max_ver): New macros.
(_AM_PYTHON_INTERPRETER_LIST): Generate this list instead of hard-coding
it. Implementation is taken from GNU Pyconfigure.