change LeafCursor to keep track of keys and values a bit more like ParentCursor does, so that KeyRef, ValueRef, and ValueLength all have to do less work, and so that LeafCursor and ParentCursor can share a bit more code.  nonetheless, it kinda seems like this caused a perf loss.  if so, need to fiugre out why.
change LeafCursor to keep track of keys and values a bit more like ParentCursor does, so that KeyRef, ValueRef, and ValueLength all have to do less work, and so that LeafCursor and ParentCursor can share a bit more code.  nonetheless, it kinda seems like this caused a perf loss.  if so, need to fiugre out why.

zumero/Elmo,zumero/Elmo