Coefficients still have .count, not .number
Accept domain, not cell argument to Constant
Count no longer optional to Argument

Also replace building of Argument directly in derivative with
TrialFunction.
Use ufl.Circumradius not cell.circumradius
Add domain if we got a finite element for family

If the user passed in a FiniteElement (for example when building
enriched function spaces) we need to add a domain argument.

This probably breaks function space caching for these cases, because the
key will be new each time.
Pass integral_type and subdomain_id out of compile_form
More domain bootstrapping

Measure objects need domain set (as well as subdomain_data).  Coordinate
function space needs its ufl element replaced by one that has correct
domain (since it is in the cache).