Use require_once() not require() in places where local/lib.php may have already included some libs

Signed-off-by: Richard Mansfield <richardm@catalyst.net.nz>

htdocs/admin/users/addtoinstitution.php

@@ -28,7 +28,7 @@
 define('INTERNAL', 1);
 define('INSTITUTIONALADMIN', 1);
 require(dirname(dirname(dirname(__FILE__))) . '/init.php');
-require('institution.php');
+require_once('institution.php');
 
 $id          = param_integer('id');
 $institution = new Institution(param_alpha('institution'));

htdocs/group/mygroups.php

@@ -33,7 +33,7 @@ define('TITLE', get_string('mygroups'));
 define('SECTION_PLUGINTYPE', 'core');
 define('SECTION_PLUGINNAME', 'group');
 define('SECTION_PAGE', 'mygroups');
-require('group.php');
+require_once('group.php');
 $filter = param_alpha('filter', 'all');
 $offset = param_integer('offset', 'all');