rank fails over ZZ because codim needs Generic => true

[mahrud]

The problem is that there's no way to pass Generic => true to codim via rank.

i1 : R = ZZ[x];

i2 : rank coker vars R
stdio:2:4:(3): error: codim: expected an affine ring (consider Generic=>true to work over QQ)

i3 : options rank

i4 : options \ methods rank

o4 = {0 => null}
     {1 => null}
     {2 => null}
     {3 => null}
     {4 => null}