Function: polrootsmod
Section: polynomials
C-Name: rootmod0
Prototype: GGD0,L,
Help: polrootsmod(pol,p,{flag=0}): roots mod the prime p of the polynomial pol. flag is
 optional, and can be 0: default, or 1: use a naive search, useful for small p.
Description:
 (pol, int, ?0):vec           rootmod($1, $2)
 (pol, int, 1):vec            rootmod2($1, $2)
 (pol, int, #small):vec       $"Bad flag in polrootsmod"
 (pol, int, small):vec        rootmod0($1, $2, $3)
Doc: row vector of roots modulo $p$ of the polynomial \var{pol}. The
 particular non-prime value $p=4$ is accepted, mainly for $2$-adic
 computations. Multiple roots are \emph{not} repeated.
 \bprog
 ? polrootsmod(x^2-1,2)
 %1 = [Mod(1, 2)]~
 ? polrootsmod(x^2-1,4)
 %2 = [Mod(1, 4), Mod(3, 4)]~
 @eprog\noindent
 If $p$ is very small, you may set $\fl=1$, which uses a naive search.
