def upload(stream, mimetype_hint=False):
    """ Replace the current contents of this file's blob with the
        contents of ``stream``.  ``mimetype_hint`` can be any of the
        folliwing:

        - ``None``, meaning don't reset the current mimetype.  This is the
          default.

        - A string containing a filename with an extension; the mimetype will
          be derived from the extension in the filename.

        - The constant :attr:`substanced.file.USE_MAGIC`, which will derive the
          content type using the ``python-magic`` library based on the
          stream's actual content.
        """
