Fix invalid MappingException 'Multiple version attributes not supported.'

In previous version, in the addAttributes, supertype attributes are cloned then added.
If the super class has a @Version field, this one is also cloned and added.

After the loop, the version field was added again (but not cloned this time), and the check done in addAttribut for version attribute for inheritance is based on ==. As the version attribute previously set was a clone of the super one, code don't satisfy the exit condition for inheritance 

Hope to be clear, and my fix is correct.