Repaired regression in Set causing Set ++ to be...
Repaired regression in Set causing Set ++ to be...

Repaired regression in Set causing Set ++ to become very expensive.
Closes #4642, no review.


slothspot/scala,scala/scala,scala/scala,felixmulder/scala,felixmulder/scala,scala/scala,lrytz/scala,scala/scala,jvican/scala,lrytz/scala,slothspot/scala,slothspot/scala,jvican/scala,martijnhoekstra/scala,jvican/scala,martijnhoekstra/scala,shimib/scala,martijnhoekstra/scala,shimib/scala,felixmulder/scala,lrytz/scala,shimib/scala,felixmulder/scala,slothspot/scala,martijnhoekstra/scala,scala/scala,shimib/scala,lrytz/scala,felixmulder/scala,slothspot/scala,shimib/scala,martijnhoekstra/scala,lrytz/scala,scala/scala,felixmulder/scala,slothspot/scala,lrytz/scala,jvican/scala,jvican/scala,jvican/scala,martijnhoekstra/scala,felixmulder/scala,shimib/scala,slothspot/scala,jvican/scala