MDL-44106 add WS_SERVER constant to all web service calls

This will help us hack around some nasty webservice problems,
such as require_login() and it will be used to set proper 'ws' origin
in logged events.

lib/setup.php

@@ -304,6 +304,11 @@ if (defined('WEB_CRON_EMULATED_CLI')) {
     }
 }
 
+// All web service requests have WS_SERVER == true.
+if (!defined('WS_SERVER')) {
+    define('WS_SERVER', false);
+}
+
 // Detect CLI maintenance mode - this is useful when you need to mess with database, such as during upgrades
 if (file_exists("$CFG->dataroot/climaintenance.html")) {
     if (!CLI_SCRIPT) {
@@ -745,6 +750,10 @@ if (CLI_SCRIPT) {
     // no sessions in CLI scripts possible
     define('NO_MOODLE_COOKIES', true);
 
+} else if (WS_SERVER) {
+    // No sessions possible in web services.
+    define('NO_MOODLE_COOKIES', true);
+
 } else if (!defined('NO_MOODLE_COOKIES')) {
     if (empty($CFG->version) or $CFG->version < 2009011900) {
         // no session before sessions table gets created