Reuse the skiplist's stack needed by insert_compare() by growing it with adds.
Rename the "replace" argument as "add" (negating the boolean) to avoid confusion
since the skiplist never replaces any element (add or preserve semantic).


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1611184 13f79535-47bb-0310-9956-ffa450edef68
Don't grow the skiplist's height if the element is finally not inserted (preserve semantic).
Do this by moving the top node creation after insertion occured, and linking to the just
inserted node(s).


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1611193 13f79535-47bb-0310-9956-ffa450edef68