Fixed low bug EXT-6825 (The border for context menu for Groups tab is...

Fixed low bug EXT-6825 (The border for context menu for Groups tab is invisible and is merged with the background) - allowed to drop shadow.
Reviewed by Vadim Savchuk at https://codereview.productengine.com/secondlife/r/248/

--HG--
branch : product-engine

indra/newview/skins/default/xui/en/menu_people_groups.xml

 <?xml version="1.0" encoding="utf-8" standalone="yes" ?>
 <menu name="menu_group_plus"
  left="0" bottom="0" visible="false"
- mouse_opaque="false" opaque="true" color="MenuDefaultBgColor" drop_shadow="false">
+ mouse_opaque="false" opaque="true" color="MenuDefaultBgColor">
   <menu_item_call
    label="View Info"
    name="View Info">