Don't let a missing constant stop us.

Sometimes when using things like expect { } and expect_error {}
you can run into an error where the constant is already removed
because it creates a whole new context (I assume, I would have
to dig deeper into RSpec Core.)
Make extensions a bit more robust.

This is done because MySQL does not support the same type of
extensions that PostgreSQL supports, so we must take this
into account and raise this fact to the user who is trying
to do this, so they can either work around it or choose to
catch it, dealers choice.