compile_elements fails for quadrilateral "HDiv Trace" elements

[jpdean]

Minimal failing example:

import ffc.codegeneration.jit
import ufl

cell = ufl.quadrilateral
element = ufl.FiniteElement("HDiv Trace", cell, 1)
compiled_element, module = ffc.codegeneration.jit.compile_elements([element])

The above fails at A = e.element.A in _evaluate_basis with AttributeError: 'HDivTrace' object has no attribute 'A'.

There appears to be a check

if isinstance(e, HDivTrace):
    return "Function not supported for Trace elements"

to prevent this occurring, but it obviously isn't working as intended.