Update specs to 3.4.9

This PR is essentially https://github.com/sass/sass-spec/pull/206. I ran into some issues rebasing #206 on master in preparation for the merge.

## Changes

Want to be good git citizen I decided against force pushing @hcatlin's branch. I'll break thing this PR into logic parts in an attempt to maintain a sane git history.

#### Spec runner

The improvements to the spec runner have been cherry picked out to https://github.com/sass/sass-spec/pull/208 and merged.

#### !global

All updates for `!global` fixes have been squash into .

#### Deleted specs

All commits removing outdated or duplicated tests have been squashed into .

#### @at-root

All `@at-root` spec updates have been squashed into .

#### House cleaning

I squashed a bunch of single line changes into a single descriptive commit sans vulgarities (for the children :wink: )

#### Formatting

#206 originally had a commit that updated the formatting of the `expected_output.css` files to match the Ruby sass. This was a big win for consistency it however had some issues which put many tests in a worse state. 

Having that commit mixed in with this PR also made diff'ing via GH impossible and I believe git history is a first-class citizen. I've opted to create https://github.com/sass/sass-spec/pull/209 to track that feature.

## Summary

**before**

```bash
734 runs, 1875 assertions, 0 failures, 0 errors, 109 skips
```

**after**

```bash
732 runs, 1824 assertions, 0 failures, 0 errors, 124 skips
```

We're now skipping a handful more specs but we now have confidence that we're developing against the intended behaviour.