Request #30075:  Forbid multiple instances of top level tools.

The Listener, Project Browser, and History tools should be unique -
they should not be duplicable.  The System and Context browsers should
only be duplicated using the Usage->DuplicateTool menu item, or by the
corresponding toolbar button, and only the duplicates should include a
number in the title.  Repeatedly choosing a menu item from the tools
menu should bring the existing tool to the front.

Also duplicates of the file viewer and the inspector tool should now 
include a number in the title of the window.

