rustc: Fix a number of stability lint holes

There are a number of holes that the stability lint did not previously cover,
including:

* Types
* Bounds on type parameters on functions and impls
* Where clauses
* Imports
* Patterns (structs and enums)

These holes have all been fixed by overriding the `visit_path` function on the
AST visitor instead of a few specialized cases. This change also necessitated a
few stability changes:

* The `collections::fmt` module is now stable (it was already supposed to be).
* The `thread_local:👿:Key` type is now stable (it was already supposed to
  be).
* The `std::rt::{begin_unwind, begin_unwind_fmt}` functions are now stable.
  These are required via the `panic!` macro.
* The `std::old_io::stdio::{println, println_args}` functions are now stable.
  These are required by the `print!` and `println!` macros.
* The `ops::{FnOnce, FnMut, Fn}` traits are now `#[stable]`. This is required to
  make bounds with these traits stable. Note that manual implementations of
  these traits are still gated by default, this stability only allows bounds
  such as `F: FnOnce()`.

Additionally, the compiler now has special logic to ignore its own generated
`__test` module for the `--test` harness in terms of stability.

Closes #8962
Closes #16360
Closes #20327

[breaking-change]

src/libtest/lib.rs

@@ -40,6 +40,7 @@
 #![feature(hash)]
 #![feature(int_uint)]
 #![feature(io)]
+#![feature(os)]
 #![feature(path)]
 #![feature(rustc_private)]
 #![feature(staged_api)]
@@ -265,7 +266,8 @@ pub fn test_main(args: &[String], tests: Vec<TestDescAndFn> ) {
 // a ~[TestDescAndFn] is used in order to effect ownership-transfer
 // semantics into parallel test runners, which in turn requires a ~[]
 // rather than a &[].
-pub fn test_main_static(args: &[String], tests: &[TestDescAndFn]) {
+pub fn test_main_static(args: env::Args, tests: &[TestDescAndFn]) {
+    let args = args.map(|s| s.into_string().unwrap()).collect::<Vec<_>>();
     let owned_tests = tests.iter().map(|t| {
         match t.testfn {
             StaticTestFn(f) => TestDescAndFn { testfn: StaticTestFn(f), desc: t.desc.clone() },
@@ -273,7 +275,7 @@ pub fn test_main_static(args: &[String], tests: &[TestDescAndFn]) {
             _ => panic!("non-static tests passed to test::test_main_static")
         }
     }).collect();
-    test_main(args, owned_tests)
+    test_main(&args, owned_tests)
 }
 
 #[derive(Copy)]