This new function can be used to dynamically switch on/off functions
in the context menu.
So far, only functions for which a comment fiels such as *MENU* or *TOGGLE*
were selected in the context menu.


git-svn-id: http://root.cern.ch/svn/root/trunk@1565 27541ba8-7e3a-0410-8455-c3a389f83636