Remove unused variable from configure.
Update to rust-layers master

Fixes accidental revert of servo/rust-layers#92.
Do not use Rust snapshot if --local-rust-root is specified.
Merge pull request #2986 from ChrisParis/cfg_local_rust_root

Do not use Rust snapshot if --local-rust-root is specified.
Merge pull request #2983 from Ms2ger/configure-unused-variable

Remove unused variable from configure.
refactor new_resource_task, use one channel instead of two
Upgrade Rust.
Merge pull request #2984 from servo/rustup-20140716

Upgrade Rust.
Merge pull request #2989 from jxs/master

refactor new_resource_task, use one channel instead of two