Add RedBlackTree tests for take/drop/slice.
Add RedBlackTree tests for take/drop/slice.

Addresses review feedback by axel22.

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