Fixed #10414 -- Make select_related fail on invalid field names.

https://code.djangoproject.com/ticket/10414

This is basically my first non-trivial contribution to Django, so it might not be perfect. I'll be happy to update the PR as required. :)
Or even go so far as to split them into three tests - one assertion per test. Then if one fails it won't prevent the other two from passing, etc.