Correct faulty reference to listener constants for Widget

Widget#addListener(int, Listener) currently states that event constants
are defined in the SWTError class, but these constants are defined in
the SWT class. This change fixes the faulty reference.

bundles/org.eclipse.swt/Eclipse SWT/cocoa/org/eclipse/swt/widgets/Widget.java

@@ -446,7 +446,7 @@ boolean resignFirstResponder (long id, long sel) {
  * be notified when an event of the given type occurs. When the
  * event does occur in the widget, the listener is notified by
  * sending it the <code>handleEvent()</code> message. The event
- * type is one of the event constants defined in class {@link SWTError}.
+ * type is one of the event constants defined in class {@link SWT}.
  *
  * @param eventType the type of event to listen for
  * @param listener the listener which should be notified when the event occurs

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/widgets/Widget.java

@@ -307,7 +307,7 @@ void _addListener (int eventType, Listener listener) {
  * be notified when an event of the given type occurs. When the
  * event does occur in the widget, the listener is notified by
  * sending it the <code>handleEvent()</code> message. The event
- * type is one of the event constants defined in class {@link SWTError}.
+ * type is one of the event constants defined in class {@link SWT}.
  *
  * @param eventType the type of event to listen for
  * @param listener the listener which should be notified when the event occurs

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Widget.java

@@ -202,7 +202,7 @@ void _removeListener (int eventType, Listener listener) {
  * be notified when an event of the given type occurs. When the
  * event does occur in the widget, the listener is notified by
  * sending it the <code>handleEvent()</code> message. The event
- * type is one of the event constants defined in class {@link SWTError}.
+ * type is one of the event constants defined in class {@link SWT}.
  *
  * @param eventType the type of event to listen for
  * @param listener the listener which should be notified when the event occurs