gf2n.rb operator/ operator%, some fixes
gf2n.rb error checks

added error checks
isPrimeFast(),test_isPrime(),GF2Poly::pow_mod
eliminated isPrime, test_isPrime

eliminated old method and test code
(fix) extend GF2n, get_prime_count
generate_minimal_prime
gf2n.rb ==
simplified methods in gf2n.rb

Fundamental functions were moved from top level into the class GF2Poly.
isPrimeFast2, test_isPrime

isPrimeFast2 is by no means fast.