patch-thread-skiplist
    lib: add skiplists; use for thread sorting by default

    Description:
	See ftp://ftp.cs.umd.edu/pub/skipLists/ for information
	about skiplists.

	Using skiplists for sorting timer threads enabled us to scale
	the timer count to the order of 1E6 on a modern x86 system
	without undue performance degradation.

	We have exercised the skiplist variant of the patch's
	thread code in bgpd for two years and believe it to
	be stable.

	Other fixes: inline timeval_cmp; handle seconds overflow
	when adding timer. Optimize thread search when not using
	skiplists.

	It still has the thread code to use skiplists under control of
	THREAD_TIMER_USE_SKIPLIST.

    Author: G. Paul Ziemba <paulz at labn.net>

See https://lists.quagga.net/pipermail/quagga-dev/2013-April/010527.html