Fixed #21504 -- Don't shadow database errors when testing for postgis version.

from django.contrib.gis.measure import Distance

from django.core.exceptions import ImproperlyConfigured

from django.db.backends.postgresql_psycopg2.base import DatabaseOperations

from django.db.utils import DatabaseError

from django.db.utils import ProgrammingError

from django.utils import six

from django.utils.functional import cached_property

        else:

            try:

                vtup = self.postgis_version_tuple()

            except DatabaseError:

            except ProgrammingError:

                raise ImproperlyConfigured(

                    'Cannot determine PostGIS version for database "%s". '

                    'GeoDjango requires at least PostGIS version 1.3. '