tests and fix for handling the fail_with handler

I just spent half of day trying to figure out why the fail handler for a Locale::Maketext package is not working. 

I think it is a bug in your plugin with $handle->fail_with(sub { $_[1] }); - it shouldn't be there.

However, I modified your tests in order to work with the modification and I hope you'll accept my pull request (this would be my first ever code contribution).