- remembering in divide_in_z() turned off (will eventually have to be replaced

  by the new remembering mechanism in remember.cpp)
- new #define options at top of source:
    USE_TRIAL_DIVISION makes divide_in_z() use trial division and Newton
      interpolation instead of recursive polynomial division (only useful
      for very large problems)
    STATISTICS enables some statistical output at the end of the program
- gcd(numeric, numeric) is now handled earlier; this should speed up normal()
- added new heuristic: gcd(p^n, p^m) with p a polynomial now immediately
  returns p^abs(n-m)
- if GCD is 1, cofactors are returned unexpanded