Refix #13844 -- Made FloatField aggregates work on Python 2.6 + Postgres

Fixed a regression introduced in 59a655988e.

django/db/backends/__init__.py

@@ -885,6 +885,8 @@ class BaseDatabaseOperations(object):
         internal_type = field.get_internal_type()
         if internal_type == 'DecimalField':
             return value
+        elif internal_type == 'FloatField':
+            return float(value)
         elif (internal_type and (internal_type.endswith('IntegerField')
                                  or internal_type == 'AutoField')):
             return int(value)