Adds the invert vertex group option to the Lattice modifier.
Adds a short flag and modifies the existing char padding for the correct amount.
Adds a .invert_vgroup to the LatticeDeformUserdata.
Passes the flag into the lattice_deform_verts function where the weights around found and used.
For the other calls of lattice_deform_verts function they pass in NULL for the flag in the same way they pass NULL for the vgroup name.