Make /contrib install/uninstall script consistent:

remove transactions
	use create or replace function
	make formatting consistent
	set search patch on first line

Add documentation on modifying *.sql to set the search patch, and
mention that major upgrades should still run the installation scripts.

Some of these issues were spotted by Tom today.

contrib/cube/cube.sql.in

@@ -1,9 +1,9 @@
--- Create the user-defined type for N-dimensional boxes
--- 
-
 -- Adjust this setting to control where the objects get created.
 SET search_path = public;
 
+-- Create the user-defined type for N-dimensional boxes
+-- 
+
 CREATE OR REPLACE FUNCTION cube_in(cstring)
 RETURNS cube
 AS 'MODULE_PATHNAME'

contrib/cube/uninstall_cube.sql

@@ -1,3 +1,4 @@
+-- Adjust this setting to control where the objects get dropped.
 SET search_path = public;
 
 DROP OPERATOR CLASS gist_cube_ops USING gist;