PIVOT-928: Always position popup menus so they stay within the screen bounds.
The existing code only did it for "context" menus, which meant that second-level
context menus (which aren't marked as such) could still stray outside the bounds.

This change means all popup menus (which could include regular menus as well as
context menus) will get positioned inside the screen bounds.

This is a merge of revision 1538840 from branches/2.0.x to trunk.



git-svn-id: https://svn.apache.org/repos/asf/pivot/trunk@1538841 13f79535-47bb-0310-9956-ffa450edef68