Provide apr_skiplist_size/height/preheight() to get the corresponding values
in O(1), and apr_skiplist_set_preheight() to configure preheight mode.


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1611515 13f79535-47bb-0310-9956-ffa450edef68
Follow up to r1611515: remove useless <limits.h> inclusion (for unused INT_MAX).


git-svn-id: https://svn.apache.org/repos/asf/apr/apr/trunk@1611517 13f79535-47bb-0310-9956-ffa450edef68