Bug 1535141

Important: if this rebase instead contains *only bug fixes,* or *only enhancements*, select the correct option from the Doc Type drop-down list. Rebase package(s) to version: rust 1.24, cargo 0.25 (will be rust 1.25 and cargo 0.26 for GA!) Highlights, important fixes, or notable enhancements: # Upstream release notes: - 1.23: https://blog.rust-lang.org/2018/01/04/Rust-1.23.html - 1.24: https://blog.rust-lang.org/2018/02/15/Rust-1.24.html - 1.25: TBD (note, we will update before 2018.2 GA) # Rust - Parameter copies are avoided when possible, improving performance. - Incremental compilation: The compiler can reuse artifacts from previous builds, only rebuilding portions that are affected by newly changed code. - Compilation now uses 16 codegen units by default. - Methods from the `AsciiExt` trait are now implemented directly on string and char types. (May cause `unused_imports` warnings if you were already using that trait.) - Several library functions are now usable in const expressions, like `mem::size_of`. (Note: upstream also highlights rustfmt, as a preview, but I haven't packaged that yet. I will try to get this in the 1.25 update.) # Cargo - `cargo check` now supports unit tests. - `cargo install` can select a specific version. - `cargo uninstall` can remove multiple packages at once. - Debug builds now enable incremental compilation by default.