BUG in SCA detection

[Oleksandr]

> ring r;
> def E = nc_algebra(-1,0);
> setring E;
> ideal Q = twostd(z);
> Q;
Q[1]=z
> NF( x2, Q);
x2
> NF( y2, Q);
y2
> qring QQ = Q; // NOT ALL SQUARES in Q!!!
> QQ;
//   characteristic : 32003
//   number of vars : 3
//        block   1 : ordering dp
//                  : names    x y z 
//        block   2 : ordering C
//   noncommutative relations:
//    yx=-xy
//    zx=-xz
//    zy=-yz
//   noncommutative type:5   /// SCA
//      is skew constant:1
//                 ncref:1
//               commref:1
//               baseref:1
//   alternating variables: [1, 3] // ALL SQUARES???
//   quotient of sca by ideal
scaQ[1]=z
// quotient ring from ideal
_[1]=z

seems that SCA detection is wrong in checking for squares of anti-commutative variables...

[Oleksandr]

wrong handling of factors of sca lead to wrong sca detection. seems to be fixed now.

TODO: check all possible usage cases... later on...