make leading ideals automatically inherit the "isSB" attribute

[ren]

I hope it won't break existing code, but I would like the output of "lead()" to inherit the isSB attribute, so that I don't need to set it manually when trying to suppress the "<ideal> is no standard basis" warning.

                     SINGULAR                                 /  Development
 A Computer Algebra System for Polynomial Computations       /   version 4.0.0
                                                           0<
 by: W. Decker, G.-M. Greuel, G. Pfister, H. Schoenemann     \   Dec 2013
FB Mathematik der Universitaet, D-67653 Kaiserslautern        \
> ring r;
> ideal I = x,y;
> I = std(I);
> attrib(I,"isSB");
1
> ideal LI = lead(I);
> attrib(LI,"isSB");
0
> reduce(I,LI);
// ** LI is no standard basis
_[1]=0
_[2]=0

[hannes]

impl. with d96d7d96a46e01e76226f7679bb1bfc06e1991b8