backport r1604596,1604598 from trunk:

    Add a basic skiplist test.  Based on test program posted to PR 56654 by Takashi Sato.

    Submitted By: Takashi Sato, covener
    Committed By: covener


    apr_skiplist becomes corrupt when nodes are reused.

    Submitted By: Takashi Sato <takashi tks st>, covener
    committed By: covener



git-svn-id: https://svn.apache.org/repos/asf/apr/apr/branches/1.5.x@1605769 13f79535-47bb-0310-9956-ffa450edef68