coding style
added IsPrime to CommonHomalgTableForMAGMATools

(working with Paco on divisors of linear Jacobian type)
fixed _PrepareInputForRingOfDerivations

(the base variables have to be passed as strings;
 the base variable s was passed as homalg_variable_...
 which caused a silly mistake in the computation of the
 parametric (order k) annihilator:
 AnnihilatorOfPower( 1, f, "s" ) );