disable JIT and parallel execution for osm2pgsql updates again

The gazetteer output doesn't disable these functions when
writing to the place table but the triggers may contain
operations that cause misplanning for the query planner.

nominatim/db/connection.py

@@ -50,6 +50,15 @@ class _Connection(psycopg2.extensions.connection):
                                 WHERE tablename = %s""", (table, ))
             return num == 1
 
+    def server_version_tuple(self):
+        """ Return the server version as a tuple of (major, minor).
+            Converts correctly for pre-10 and post-10 PostgreSQL versions.
+        """
+        version = self.server_version
+        if version < 100000:
+            return (version / 10000, (version % 10000) / 100)
+
+        return (version / 10000, version % 10000)
 
 def connect(dsn):
     """ Open a connection to the database using the specialised connection