0003513: There is no check for boundary of array in method Set for array attributes

- Added check of array's boundary in Set(i, val) methods.
- Added comments to cdl files.
- removed accidental modification in TDataStd_ExtStringArray::Value(i).
- recovering accidentally lost modifications.

src/TDataStd/TDataStd_ByteArray.cxx

@@ -79,6 +79,8 @@ Handle(TDataStd_ByteArray) TDataStd_ByteArray::Set(const TDF_Label&       label,
 void TDataStd_ByteArray::SetValue (const Standard_Integer index,
 				   const Standard_Byte value) 
 {
+  if (myValue.IsNull()) 
+    return;
   if (value == myValue->Value(index))
     return;
   Backup();