catchi negative arguments for monomial

[gorzel]

The command monomial should return 0, if the intvec contains negative entries. Compare with this default behaviour:

> ring r=0,(x,y,z),dp;
> x^(-2);    // OK 
0

Then

> monomial(intvec(3,2,1));    // OK
x3y2z
> monomial(intvec(3,-2,1));  // This should give 0
x3y65534z65535
 
> monomial(intvec(3,2,1,4));    // OK
x3y2z*gen(4)
> monomial(intvec(3,2,1,0));    // OK
x3y2z

> monomial(intvec(3,2,1,-4));    // Make no sense,
x3y2z*gen(-4)                    // should give 0 or x3y2z

[hannes]

negative entries causes an error.