Modules: use public API

Avoid accessing protected member variables directly, so
there's a chance of cleaning up the module API later.

modules/cyrusauth.cpp

@@ -44,7 +44,7 @@ public:
 	}
 
 	void OnModCommand(const CString& sCommand) {
-		if (m_pUser->IsAdmin()) {
+		if (GetUser()->IsAdmin()) {
 			HandleCommand(sCommand);
 		} else {
 			PutModule("Access denied");