[1.6.x] Fixed #20224 -- Update docs examples which mention __unicode__

Thanks Marc Tamlyn and Tim Graham for the review.
Backport of 7442eb1a24 from master.

docs/ref/contrib/gis/commands.txt

@@ -65,8 +65,8 @@ of using ``ogrinspect`` :ref:`in the tutorial <ogrinspect-intro>`.
 
 .. django-admin-option:: --name-field <name_field>
 
-   Generates a ``__unicode__`` routine on the model that will return the
-   the given field name.
+   Generates a ``__unicode__`` routine (``__str__`` on Python 3) on the model
+   that will return the the given field name.
 
 .. django-admin-option:: --no-imports
 

docs/ref/contrib/gis/layermapping.txt

@@ -60,6 +60,8 @@ Example
         name = models.CharField(max_length=25) # corresponds to the 'str' field
         poly = models.PolygonField(srid=4269) # we want our model in a different SRID
         objects = models.GeoManager()
+
+        # On Python 3: def __str__(self):
         def __unicode__(self):
             return 'Name: %s' % self.name
 

docs/ref/contrib/gis/tutorial.txt

@@ -244,6 +244,7 @@ model to represent this data::
         objects = models.GeoManager()
 
         # Returns the string representation of the model.
+        # On Python 3: def __str__(self):
         def __unicode__(self):
             return self.name