fsplay fixed and unit tested

[email protected]/hackerlab--splay--1.0--patch-2

I completely rewrote fsplay_raise based on D. Sleator's public domain
implementation.  A few little hacks and I was able to not only make it
(pseudo) functional, but also keep it an iterative process (rather
than degrade to recursion like an earlier attempt).  I also copied
Sleator's unit tests so we can have a little verification.

I'm a little unsure about my uses of fsplay_(un)ref in the code and
tests so if someone would volunteer to take a look, that would be
great.  Besides that, however, I'm rather confident in its
correctness.  Sorry for not being great about including diagrams in
all of the new code either.

Tom, lemme know if I should clean anything up before you're willing to
merge it.

-jivera