[racket-dev] New plot library pushed

I've just pushed the new 'plot' library.

Eli and I both forgot that the new 'plot' still needs the old libfit, 
and removed it along with libplplot. I just added libfit back (the 
sources are in "src/fit" now instead of "src/plot/fit") along with the 
proper configure, Makefile.in, and get-libs.rkt changes.

I can verify that libfit compiles on 64-bit Ubuntu. It *should* build on 
Windows and Mac. :D

I've taken Matthew's suggestion to make the new 'plot' as 
backward-compatible as possible. Plots might still break (such as the 
example at racket-lang.org and on the Wikipedia page). Using the 
'plot/compat' module should make these work.

This change replaces about 20000 lines of C+support code with 7000 lines 
of Racket that does a lot more. Racket code for backward compatibility 
totals only 500 lines. The libfit library is about 500 lines of C+make code.

Neil T