* Remove reserved_reg functionality.
This wasn't implemented, and if we need it in the future, it seems like
it would be better to extend the concept of global values to cover this.
* Use GlobalValue::reserved_value() for sentinal values.
* Update to rustfmt-preview.
* Run "cargo fmt --all" with rustfmt 0.4.1.
rustfmt 0.4.1 is the latest release of rustfmt-preview available on the
stable channel.
* Fix a long line that rustfmt 0.4.1 can't handle.
* Remove unneeded commas left behind by rustfmt.