Delete operations should offer the possibility to not undo deletions

When you add a Delete operation in a script file, the corresponding undo method is to restore the backup file.

Sometimes, we want not to have this behaviour (for example in the case of a temporary file we managed).

It is not possible for the moment.

The strange thing is that it has been partially implemented in the framework: when an operation Delete is created, a "performUndo" flag is set to false for the operation. But this flag is never used.