Fix some bugs with ordering_negative_numbers.

- Sort numbers numerically
- Correctly ensure we don't start out already sorted
- Don't grade answer if nothing has changed

Test plan:
    Ensure http://localhost:8000/exercises/ordering_negative_numbers.html?debug&problem=0&seed=77 doesn't start out sorted
    Ensure http://localhost:8000/exercises/ordering_negative_numbers.html?debug&problem=0&seed=11 accepts the correct answer
    Ensure http://localhost:8000/exercises/ordering_negative_numbers.html?debug&problem=0&seed=44 accepts the correct answer
    Also ensure click check answer doesn't mark you wrong until you do something.

Auditors: peter