`Quantity.opBinary` not working when called from a const function.

[LiamM32]

Here is my function where I got this error:

    Millimolar getConcentration(Compound chemical) const {
        return (ligandLevels[chemical].inBody / body.bloodVolume);
    }

I got the following error:

Error: incompatible types for `(this.ligandLevels[chemical].inBody) / (this.body.bloodVolume)`: `const(Quantity!(PrefixedUnit!(BaseUnit!("mole", "mol"), -3, __T12PrefixSystemVli10S_D12experimental5units2si10__lambda53FNaNbNfZASQBtQBi6PrefixZ), float))` and `const(Quantity!(BaseUnit!("litre", "L"), float))`

Removing the const attribute of this function results in the error disappearing.

This should be resolved so that arithmetic on Quantity values can be done in constant functions.