Package rpm-build-python: Information

- python.compileall.py:
  + removed python version <= 2.2 py_compile workaround;
  + fixed file executability check (by iv@).
- python.{prov,req}.files:
  + enhanced "python script text executable" type check;
  + added is_python3_path check from python.{prov,req}.py,
    which is now applied only to files of uncertain type.
- python.{prov,req}.py: removed is_python3 check.
- brp-bytecompile_python:
  added $RPM_PYTHON3_COMPILE_INCLUDE to the exclude list (closes: #28606).

- python.{prov,req}.files: reintroduced optimization from 0.36.0-alt3.
- python.prov.files: skip all files that cannot be provided due to
  rpmbuild restrictions.

- Take %_python3_path into account