folder_block_ops: comments for dir cache functions, and cleanup
folder_block_ops: comments for dir cache functions, and cleanup

Issue: KBFS-2071

keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/client