separate square-free and degree separation algorithms

* for polynomial factorisation over finite fields
* at the moment just for fields with prime cardinality
move the ocre functionality of fill-array into own function

* because this sort of thing is multi-dimension iteration, with can be
  considered as very useful for other problems.
implement baby-step, giant-step
Merge branch 'poly-factorisation' of sl2z.de:olaf/math-utils into poly-factorisation
move polynomial printing code to math-formatter
restore `var' slot for power series for unification between polys and series
introduce a common root object for complex math types
memoisation defun changed its name
factorise integers over a set of smooth primes
import symbol from generic-math