Changed GeoDjango GeometryField to lazily load units, units_name and _spheroid

        # Setting the SRID and getting the units.  Unit information must be

        # easily available in the field instance for distance queries.

        self.srid = srid

        self.units, self.units_name, self._spheroid = get_srid_info(srid)

        # units_cache, units_name_cache and _spheroid_cache are lazily loaded.

        self._units_cache = self._units_name_cache = self._spheroid_cache = None

        # Setting the dimension of the geometry field.

        self.dim = dim

        super(GeometryField, self).__init__(**kwargs) # Calling the parent initializtion function

    def _populate_srid_info(self):

        self._units_cache, self._units_name_cache, self._spheroid_cache = get_srid_info(self.srid)

    def _get_units(self):

        if self._units_cache is None:

            self._populate_srid_info()

        return self._units_cache

    units = property(_get_units)

    def _get_units_name(self):

        if self._units_name_cache is None:

            self._populate_srid_info()

        return self._units_name_cache

    units_name = property(_get_units_name)

    def _get_spheroid(self):

        if self._spheroid_cache is None:

            self._populate_srid_info()

        return self._spheroid_cache

    _spheroid = property(_get_spheroid)

    # The following properties are for formerly private variables that are now

    # public for GeometryField.  Because of their use by third-party applications,

    # a deprecation warning is issued to notify them to use new attribute name.