Add search_path setting line.

All contrib modules have this line, and it being there make it easier to treat
the temporal module like other extensions in terms of changing that line for
installing it into a different schema.

period.sql.in

@@ -5,6 +5,9 @@
 -- Portions Copyright (c) 2007-2008, Jeff Davis <[email protected]>
 --
 
+-- Adjust this setting to control where the objects get created.
+SET search_path = public;
+
 CREATE TYPE period;
 
 CREATE OR REPLACE FUNCTION period_in(cstring) RETURNS period LANGUAGE C IMMUTABLE STRICT