(MDL-8973) Fix OOP model of new multi auth plugins + some other auth related fixes, fixed change_password, ldap updates, etc.; TODO: fix docs

backported from HEAD

lib/accesslib.php

@@ -2194,9 +2194,10 @@ function role_assign($roleid, $userid, $groupid, $contextid, $timestart=0, $time
  * @param $userid
  * @param $groupid
  * @param $contextid
+ * @param $enrol unassign only if enrolment type matches, NULL means anything
  * @return boolean - success or failure
  */
-function role_unassign($roleid=0, $userid=0, $groupid=0, $contextid=0) {
+function role_unassign($roleid=0, $userid=0, $groupid=0, $contextid=0, $enrol=NULL) {
 
     global $USER, $CFG;
 
@@ -2209,6 +2210,9 @@ function role_unassign($roleid=0, $userid=0, $groupid=0, $contextid=0) {
             $select[] = $arg.' = '.$$arg;
         }
     }
+    if (!empty($enrol)) {
+        $select[] = "enrol='$enrol'";
+    }
 
     if ($select) {
         if ($ras = get_records_select('role_assignments', implode(' AND ', $select))) {