Function: bnrclassno
Section: number_fields
C-Name: bnrclassno
Prototype: GG
Help: bnrclassno(bnf,I): ray class number of the module I for the big number
 field bnf. Faster than bnrinit if only the ray class number is wanted.
Doc: $\var{bnf}$ being as output by
 \kbd{bnfinit} (units are mandatory unless the ideal is trivial), and $I$
 being a modulus, computes the ray class number of the number field for the
 modulus $I$. One can input the associated \var{bid} for $I$ instead of the
 module itself, saving some time.

 This function is faster than \kbd{bnrinit} and should be used if only the
 ray class number is desired. See \tet{bnrclassnolist} if you need ray class
 numbers for all moduli less than some bound.
