Cloning Class in SDF Provider Fails

[gregboone]

The scenario under which this defect occurs has to deal with a join between 2 Feature Source where one or both have pre-defined calculated properties. When the joined class definitions were being combined and pruned in the SDF provider, the calculated properties had already been added. When the properties were added a second time, an exception was thrown identifying the added property as a duplicate.

The solution here is to check if the calculated property has already been added before re-adding it.