Commits on Aug 31, 2017

1. Switch back to pinning Rust by Nightly date instead of commit hash… …

   … this time using a `rust-toolchain` file compatible with rustup:
   https://github.com/rust-lang-nursery/rustup.rs/#the-toolchain-file
   
   And upgrade to rustc 1.21.0-nightly (c11f689d2 2017-08-29)
   
   ----
   
   Now if both `system-rust` and `system-cargo` are set to `true` in `.servobuild`’s `[tools]` section,
   and the corresponding `rustc` and `cargo` binaries are in fact rustup’s wrappers,
   then rustup will use the correct version based on `rust-toolchain`.
   
   CC #11361
   
   Unlike #17927,
   this does not make mach use rustup directly.

   

   SimonSapin committed Aug 31, 2017

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