8072817: CardTableExtension kind() should be BarrierSet::CardTableExtension
Summary: Use BarrierSet::CardTableForRS where needed, and update concrete bs tags.
Reviewed-by: jwilhelm, jmasa

8130931: Refactor CardTableModRefBS[ForCTRS]
Summary: Remove friends and push CTRS-specific code down from base to derived
Reviewed-by: tschatzl, mgerdin