Exception stringification followup

[uuf6429]

This is the follow up for #1421 (comment)

On a side note, I'm wondering if supportsException should also check for the stringification classes.
Although its name relates to the exception, the usage actually relates to if it can stringify an exception or not.

[ciaranmcnulty]

Thanks @uuf6429 I like the idea to add an exception, but not a fan of the change to a switch/case

I'll try and look at the test suite and add something to the matrix that would have caught the issue before #1422 was merged, so we can check that this change is preserving the same behaviour

[uuf6429]

but not a fan of the change to a switch/case

I find that it is very readable once you get used to the concept; it keeps the cause-and-effect very close.
My personal policy on the matter is that anything more than two if conditions (with direct returns and an else) is more suited to a switch.

I agree about a test, but I'm not sure how you can do such a test in practice (since it depends on (non-)existence of classes).