Fix quoting in help messages in uuid-ossp extension scripts.

The command we're telling people to type needs to include double-quoting
around the unfortunately-chosen extension name.  Twiddle the textual
quoting so that it looks somewhat sane.  Per gripe from roadrunner6.

contrib/uuid-ossp/uuid-ossp--1.0.sql

@@ -1,7 +1,7 @@
 /* contrib/uuid-ossp/uuid-ossp--1.0.sql */
 
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
-\echo Use "CREATE EXTENSION uuid-ossp" to load this file. \quit
+\echo Use '''CREATE EXTENSION "uuid-ossp"''' to load this file. \quit
 
 CREATE FUNCTION uuid_nil()
 RETURNS uuid

contrib/uuid-ossp/uuid-ossp--unpackaged--1.0.sql

@@ -1,7 +1,7 @@
 /* contrib/uuid-ossp/uuid-ossp--unpackaged--1.0.sql */
 
 -- complain if script is sourced in psql, rather than via CREATE EXTENSION
-\echo Use "CREATE EXTENSION uuid-ossp" to load this file. \quit
+\echo Use '''CREATE EXTENSION "uuid-ossp"''' to load this file. \quit
 
 ALTER EXTENSION "uuid-ossp" ADD function uuid_nil();
 ALTER EXTENSION "uuid-ossp" ADD function uuid_ns_dns();