Wrong saturation exponent

Regression in 4.3.2p3:
```
> LIB "elim.lib";
> ring r = 0,(x,y,z),dp;
> ideal i = x^5*z^3, x*y*z, y*z^4;
> ideal j = z;
> sat(i,j);
[1]:
   _[1]=y
   _[2]=x5
[2]:
   0
```
with 4.3.2p2:
```
> sat(i,j);
[1]:
   _[1]=y
   _[2]=x5
[2]:
   4
```