Assert that readOnly isn't called over CPs with setter

[cibernox]

In preparation for emberjs/rfcs#12

Ensure that an error is thrown is readOnly is invoked over CP's that defines a setter function. It is conceptually absurd.

[rwjblue]

Needs to use expectAssertion (because prod build tests will not throw since asserts are removed from prod builds).

[rwjblue]

This seems ok, but I don't understand what it is for...

[cibernox]

The last ok? I've seen similar lines in other tests related to assertions, but I agree that is redundant. Gone

[rwjblue]

Thank you!

[tomdale]

This should not generate an exception, as this is a breaking change that causes apps that happened to have an extra unused argument in their CP functions to break. We can deprecate it in 1.x and cause it to raise in 2.x.

[cibernox]

I haven't considered that, you're right, it's beaking.
However, I think I can fix it by adding to the assertion that the getter and the setter are not the same function. That way the assert will not be fired with the old syntax.