Quick fix for infinite loop and bugs in Cantor-Zassenhaus implementation.
Correction for previous commit fixing Cantor-Zassenhaus.
Further little improvements for Cantor-Zassenhaus.
Add a few tests for Cantor-Zassenhaus fixes.
Fix previous doctests for Cantor-Zassenhaus.
Better syntax for Cantor-Zassenhaus doctest.
Better use of modular exponentiation in Cantor-Zassenhaus + sig_on magic.
Add examples for Cantor-Zassenhaus.
Another try for Cantor-Zassenhaus without si_on/off.
Add sig_on magic for NTL polynomial exponentiation.
Trac #16162: Cantor-Zassenhaus may enter infinite loop over GF(2**k) and cannot be interrupted

A solution is to use random polynomials just as for odd characteristic.

This also replaces calls to `power_mod` by calls to `pow` with three
arguments which uses implementation optimized code for modular
exponentiation.

URL: http://trac.sagemath.org/16162
Reported by: jpflori
Ticket author(s): Jean-Pierre Flori
Reviewer(s): Peter Bruin