Remove temporary wptrunner hotfix.

This was added in anticipation of a wptrunner release that includes the change.
Update wptrunner to version 1.2.
auto merge of #3476 : Ms2ger/servo/rm-hotfix, r=Ms2ger,metajack

This was added in anticipation of a wptrunner release that includes the change.
Don't move the data when extracting the bytes in XMLHttpRequest::Send.

The data is used later to set the Content-Type header. Current rustc
(4d2af3861) does not detect this use-after-move, but treats the later use as
if the data was None. It will, however, detect the bug in d2b30f7d3, which we
are upgrading to.
auto merge of #3522 : Ms2ger/servo/xhr-send-uaf, r=SimonSapin

The data is used later to set the Content-Type header. Current rustc
(4d2af3861) does not detect this use-after-move, but treats the later use as
if the data was None. It will, however, detect the bug in d2b30f7d3, which we
are upgrading to.
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