Code holiday commit:

- fix: user pref, window title was reset to 'Blender' on tab usage

- Undo history menu back:
  - name "Undo History"
  - hotkey alt+ctrl+z (alt+apple+z for mac)
  - works like 2.4x, only for global undo, editmode and particle edit.

- Menu scroll
  - for small windows or screens, popup menus now allow to display
    all items, using internal scrolling
  - works with a timer, scrolling 10 items per second when mouse 
    is over the top or bottom arrow
  - if menu is too big to display, it now draws to top or bottom, 
    based on largest available space.
  - also works for hotkey driven pop up menus.

- User pref "DPI" follows widget/layout size
  - widgets & headers now become bigger and smaller, to match 
    'dpi' font sizes. Works well to match UI to monitor size.
  - note that icons can get fuzzy, we need better mipmaps for it

source/blender/editors/interface/interface_widgets.c

@@ -771,7 +771,7 @@ static void widget_draw_preview(BIFIconID icon, float UNUSED(alpha), rcti *rect)
 
 
 /* icons have been standardized... and this call draws in untransformed coordinates */
-#define ICON_HEIGHT		16.0f
+#define ICON_HEIGHT		UI_DPI_FAC*16.0f
 
 static void widget_draw_icon(uiBut *but, BIFIconID icon, float alpha, rcti *rect)
 {
@@ -3081,6 +3081,18 @@ void ui_draw_menu_back(uiStyle *UNUSED(style), uiBlock *block, rcti *rect)
 	else
 		wt->draw(&wt->wcol, rect, 0, 0);
 	
+	if(block) {
+		if(block->flag & UI_BLOCK_CLIPTOP) {
+			/* XXX no scaling for UI here yet */
+			glColor3ubv((unsigned char*)wt->wcol.text);
+			UI_DrawTriIcon((rect->xmax+rect->xmin)/2, rect->ymax-8, 't');
+		}
+		if(block->flag & UI_BLOCK_CLIPBOTTOM) {
+			/* XXX no scaling for UI here yet */
+			glColor3ubv((unsigned char*)wt->wcol.text);
+			UI_DrawTriIcon((rect->xmax+rect->xmin)/2, rect->ymin+10, 'v');
+		}
+	}	
 }
 
 void ui_draw_search_back(uiStyle *UNUSED(style), uiBlock *block, rcti *rect)