Issue #3080: Use Unicode to import source and compiled modules

* Use Unicode for module name and path in the following functions:

   * get_file()
   * load_source_module(), parse_source_module()
   * make_compiled_pathname(), check_compiled_module(),
     read_compiled_module(), load_compiled_module(), write_compiled_module(),
     update_compiled_module()

 * On Windows, use CreateDirectoryW() instead of mkdir()
 * update_compiled_module() cannot fail anymore