[CM] Snd 20.4

[bil at ccrma.Stanford.EDU]

Snd 20.4:

s7: added s7_scheme* argument to s7_is_eqv, and all the 
s7_set_*_function calls that
       set optimizer functions (the preceding calls were, sadly, not 
thread-safe).
     libarb_s7.c: a multiprecision library paralleling GSL.  Requires 
libflint.
       Only in the gmp version of s7. (I wanted multiprecision Bessel 
functions).

checked: ubuntu 20.04, sbcl-2.0.4, FC 32, gsl 2.6, Ruby 2.7, gcc/clang 
10

Thanks!: Elijah, Woody Douglass, Ian Duncan, Kjetil Matheussen