0025093: Visualization - deletion of SelectMgr_SelectableObject does not invalidate owners

-Unstaged useless changes from CR0025093
-Now handles to Entity_owner are nullified in SelectMgr_Selection destructor

-Code formatting

src/SelectMgr/SelectMgr_Selection.cdl

@@ -68,6 +68,12 @@ is
     	--- Purpose: Constructs a selection object defined by the selection mode IdMode.
     	-- The default setting 0 is the selection mode for a shape in its entirety.   
 
+    Destroy (me : mutable) is static;
+        ---Level: Public
+        ---Purpose:
+        ---Category: Methods to modify the class definition
+        ---C++: alias ~
+
     Add  (me         : mutable;
     	  aprimitive : SensitiveEntity from SelectBasics) 
     	---Purpose: Adds the sensitive primitive aprimitive to the list of

src/SelectMgr/SelectMgr_Selection.cxx

@@ -25,6 +25,19 @@ SelectMgr_Selection
 ::SelectMgr_Selection (const Standard_Integer IdMode):
 myMode(IdMode)
 {}
+
+//==================================================
+// Function: Destroy
+// Purpose :
+//==================================================
+void SelectMgr_Selection::Destroy()
+{
+  for (SelectBasics_ListIteratorOfListOfSensitive anIt(myentities); anIt.More(); anIt.Next())
+  {
+    anIt.Value()->Set (NULL);
+  }
+}
+
 //==================================================
 // Function: ADD
 // Purpose :