Compute coverage with negated statements

### Story ###
- https://www.pivotaltracker.com/story/show/77141298

### Notes ###
- use ```result``` rationale instead of updatedRationale when computing coverage
  - updatedRationale ignores specific occurrences that are not true, so to achieve coverage you would need a valid path within the patient population for coverage to compute accurately

### Screenshot ###
![screen shot 2014-08-19 at 3 04 28 pm](https://cloud.githubusercontent.com/assets/456952/3971449/db928dd2-27d3-11e4-8cb5-6003900c297b.png)