Tools/python: Extending python tool

add: show more command-line arguments to control which
     python is used and where py/pyext files should be installed.
     The new options are in addition to the existing PYTHON, PYTHONDIR,
     and PYTHONARCHDIR environment variable, providing the help messages
     to the user, so it can easily change parameters without second-guessing
     of what are they.

     Environmental parameters override command line arguments (is it right?)

updated: An extension to Configure.find_command to allow specification
         of the name for the searched command (using `msg` option). This is
         helpful when the search command is a huge list, as in the case of
         python's python-config case.

updated: Do not specify prefix for `get_python_lib`, since this way it
         can result in a wrong PYTHONDIR and PYTHONARCHDIR on certain platforms
         (e.g., OSX)

updated: Changing logic with byte-compilation of python files. Mow, files are
         compiled during the build stage, not install stage.  During the
         install stage files are simply copied to the requested
         location.

updated: If there is an error in python source code, byte-compilation
         phase will raise an exception and abort building process.
extras/doxygen: Adding support for RECURSIVE and making detection non-mandatory by default

added: support for RECURSIVE, as well as for included and excluded files

changed: detection of doxygen is non-mandatory by default. If it is
         desired that doxygen is mandatory, user is expected to check
         bld|conf.env.DOXYGEN and bld|conf.env.TAR variables