Upgrade to rustc d2b30f7d3 2014-09-23
Enable rustdoc for the style crate. Fix #2924.

We’re now at a Rust version that has a fix for
https://github.com/rust-lang/rust/issues/16274
Add a 'mach rust-root' command.
Have the Rust snapshot directory include the Rust version and hash.

That way, whenever rust-snapshot-hash changes, mach will look for
the Rust snapshot in a different directory and re-boostrap as needed.

However, older rust version will be left behind never cleaned up.
This is good for git-bisect, but not for disk space:
the current snapshot is 618 MB.

In the future, we may want `mach clean` or some other comment
to remove unused Rust snapshots.

CC #3388
auto merge of #3487 : servo/servo/rustup-20140923, r=Ms2ger

The biggest language change is that enum variants now also reserve (for future use) a name in the type namespace, which must not collide with other types. Some things were renamed, and others qualified as `module::name`.
CSS selector :enabled no longer matches Anchor, Area & Link elements

HTML spec has been modified [1] to disable support for :enabled CSS
selector on Anchor, Area & Link elements, after discussion on W3C
Bugzilla [2].

[1] https://html5.org/r/8818
[2] https://www.w3.org/Bugs/Public/show_bug.cgi?id=26622
auto merge of #3491 : brunoabinader/servo/css-selector-enabled-remove-anchor-area-link-elems, r=Ms2ger

HTML spec has been modified [1] to disable support for :enabled CSS
selector on Anchor, Area & Link elements, after discussion on W3C
Bugzilla [2].

[1] https://html5.org/r/8818
[2] https://www.w3.org/Bugs/Public/show_bug.cgi?id=26622

Next step: Move :enabled CSS selector content test to web-platform-tests.