Rollup merge of #38245 - estebank:cast-deref-hint-2, r=nikomatsakis

Rollup merge of #38245 - estebank:cast-deref-hint-2, r=nikomatsakis

When cast needs a dereference point at full cast

After the fix of #37453 in PR #37369, instead of pointing at only the cast type, point at the full cast span when a cast needs a dereference, as well as assign the error label to the correct span for proper coloring:

<img width="471" alt="error span pointing at the entire cast" src="https://cloud.githubusercontent.com/assets/1606434/21024245/8797fc2e-bd38-11e6-82c1-66c281c656c1.png">

instead of

<img width="471" alt="error span pointing at the type of the cast" src="https://cloud.githubusercontent.com/assets/1606434/21023777/d4814aa6-bd36-11e6-9fc3-b2a0ea5ee15d.png">

Move `compile-fail` test to `ui` test.