CoordinateDerivative and Conj do not compose correctly.

suppose in a complex valued inverse problem we have:
```python

x = SpatialCoordinate(mesh)
functional = f(x)*dx
```
where `f(x)` is some UFL expression which might be a function of x. Now, the adjoint will need to compute:
```python

conj(derivative(functional, mesh)
```
Which is currently an error since `CoordinateDerivative` must be the outermost operator on any expression. If we push the `conj` inside the derivative then this is also an error because then the conjugate is not applied to the `det(J)` which results from integral scaling. In combination with the `CoordinateDerivative` this causes unconjugated test functions, which is an error.

Answers on a postcard please.