Add extra thread-related checking

* java/org/gnu/emacs/EmacsService.java (EmacsService)
(checkEmacsThread): New function.
(fillPolygon, drawRectangle, drawLine, drawPoint, copyArea)
(clearArea):
* java/org/gnu/emacs/EmacsThread.java (EmacsThread):
* java/org/gnu/emacs/EmacsView.java (EmacsView, swapBuffers):
Call where appropriate.

java/org/gnu/emacs/EmacsView.java

@@ -338,6 +338,7 @@ public final class EmacsView extends ViewGroup
   public void
   damageRect (Rect damageRect)
   {
+    EmacsService.checkEmacsThread ();
     damageRegion.union (damageRect);
   }
 
@@ -351,6 +352,10 @@ public final class EmacsView extends ViewGroup
     Rect damageRect;
     Bitmap bitmap;
 
+    /* Make sure this function is called only from the Emacs
+       thread.  */
+    EmacsService.checkEmacsThread ();
+
     damageRect = null;
 
     /* Now see if there is a damage region.  */