Bump version, upgrade bootstrap

This commit updates the version number to 1.17.0 as we're not on that version of
the nightly compiler, and at the same time this updates src/stage0.txt to
bootstrap from freshly minted beta compiler and beta Cargo.

src/librustc_lint/lib.rs

@@ -31,6 +31,7 @@
 #![cfg_attr(test, feature(test))]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
+#![feature(i128_type)]
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(rustc_private)]
@@ -46,8 +47,6 @@ extern crate rustc_back;
 extern crate rustc_const_eval;
 extern crate syntax_pos;
 
-extern crate rustc_i128;
-
 pub use rustc::lint;
 pub use rustc::middle;
 pub use rustc::session;