[451547 ] contextMenu on multiselection on navigator tree not supported
    
    The use case is to be able to select treeitem on navigator view for
    instance, in different directories and then call the contextMenu,
    to perform a "Compare with each other" action on the selected items.
    

Change-Id: I646a08410d9a018d37c044adfcf83430ce8af478
Signed-off-by: Stephane Bouchet <stephane.bouchet@intel.com>
Bug: https://bugs.eclipse.org/451547