Add database comments to template0 and postgres databases, and improve

the comments on the template1 database.  No catalog version bump because
they are just comments.

src/bin/initdb/initdb.c

@@ -1976,6 +1976,8 @@ make_template0(void)
 		"REVOKE CREATE,TEMPORARY ON DATABASE template1 FROM public;\n",
 		"REVOKE CREATE,TEMPORARY ON DATABASE template0 FROM public;\n",
 
+		"COMMENT ON DATABASE template0 IS 'unmodifiable empty database';\n",
+
 		/*
 		 * Finally vacuum to clean up dead rows in pg_database
 		 */
@@ -2011,6 +2013,7 @@ make_postgres(void)
 	const char **line;
 	static const char *postgres_setup[] = {
 		"CREATE DATABASE postgres;\n",
+		"COMMENT ON DATABASE postgres IS 'default administrative connection database';\n",
 		NULL
 	};
 

src/include/catalog/pg_database.h

@@ -71,7 +71,7 @@ typedef FormData_pg_database *Form_pg_database;
 #define Anum_pg_database_datacl			12
 
 DATA(insert OID = 1 (  template1 PGUID ENCODING "LC_COLLATE" "LC_CTYPE" t t -1 0 0 1663 _null_));
-SHDESCR("default template database");
+SHDESCR("default template for new databases");
 #define TemplateDbOid			1
 
 #endif   /* PG_DATABASE_H */