UnicodeError fix for _stimulus.py

gistfile1.txt

    def __init__(self, log_comment=None):
        """Create a stimulus.

        Keyword arguments:
        log_comment -- the comment for the event log file (str) (optional)

        """

        self._id = Stimulus._id_counter
        Stimulus._id_counter += 1

        log_txt = "Stimulus,created,{0},{1}".format(self.id,
                                                    self.__class__.__name__)
        if log_comment is not None:
            # Hack to avoid Unicode errors when Expyriment is placed in a
            # location that contains special characters.
            if isinstance(log_comment, str):
                import sys
                log_comment = log_comment.decode(sys.getfilesystemencoding())
            log_txt = u"{0},{1}".format(log_txt, log_comment)
        expyriment._active_exp._event_file_log(log_txt, 2)