Jacobi symbol using Lehmer's algorithm.

[Torbjorn Granlund]

bodrato at mail.dm.unipi.it writes:

  For sure their speed are comparable. That's why I decided to run a test
  comparing _results_ given by the two sub-quadratic codes (with even a and
  odd b), they hopefully do not share the same bugs. No differences have
  been found, yet.
  
I would suggest to make use of the --enable-minithres mechanism, and
then stick to operands that are not terribly large.

-- 
Torbjörn