elative mod path from the one passed in.

If the filename is no in path_to_check, returns None

Note this function will look for both abs and realpath of the file,
this allows to find the relative base path even if the file is a
symlink of a file in the passed in path

Examples:
    _get_relative_base_path("/a/b/c/d.py", "/a/b") ->  ["c","d"]
    _get_relative_base_path("/a/b/c/d.py", "/dev") ->  None
Nr