Returns a list of all the builtins being used in *tokens*.

def enumerate_builtins(tokens):
    """
    Returns a list of all the builtins being used in *tokens*.
    """
    out = []
    for index, tok in enumerate(tokens):
        token_type = tok[0]
        token_string = tok[1]
        if token_string in builtins:
            # Note: I need to test if print can be replaced in Python 3
            special_special = ['print'] # Print is special in Python 2
            if py3:
                special_special = []
            if token_string not in special_special:
                if not token_string.startswith('__'): # Don't count magic funcs
                    if tokens[index-1][1] != '.' and tokens[index+1][1] != '=':
                        if token_string not in out:
                            out.append(token_string)
    return out