Previously tests would not fail if they encountered an error such as
LineOverflow or TrailingWhitespace. Making the tests error out will fix
this mismatch between running rustfmt for real and running the tests.
This also modifies all tests that previously contained errors so that
they no longer contain errors (in almost all of the tests this is
accomplished by setting error_on_line_overflow = false).
Only change multiline comments of the form
```rust
/*
* Text
*/
```
while not affecting comments of the form
```rust
/*
Text
*/
```
when normalize_comments is off. In the first case,
we have a known character we can align against, while
we don't have one in the second case.
Before, we have converted the second form into the first,
but this is against the spirit of normalize_comments being
turned off.
Fixes#956
