Sheaves

New Features:

• ZeroSubscheme returns the vanishing subscheme for a global section of a locally free sheaf.
• HorrocksMumfordBundle returns the Horrocks-Mumford bundle on projective 4-space as a locally free sheaf of rank 2.
• Restriction gives the pullback of a sheaf to a subscheme.

Changes:

• IsLocallyFree has finally been fixed (thanks to Eric Rains for pointing out the bug). It has been re-implemented using Fitting ideals with an adaptation of the old method as an alternative. The latter now computes an ëtale stratification and applies the old method inductively down it.