Package rpm-build-python: Information

- Assume that setuptools are required if the traditional Python build/install
  macros are used (overridable through %python_setup_buildrequires).

  The idea is that the Build Root Policy scripts for Python are executed
  unconditionally whenever python is present in the system, but the
  setuptools requirement is optional. (As a consequence, there may be a
  working system with Python without setuptools, because setuptools
  are not used at runtime.)

- Added macro python_version_nodots for retrieving python version
  in format 'MajorMinor' without dot delimiter.

- Fix bug when file may be skipped during 'provides' and 'requires' calculations
  if file is located in %python_sitelibdir and file name starts with 'python3'.