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::imp::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]

1 files changed, 2 insertions, 0 deletions

diff --git a/src/libstd/rt/unwind.rs b/src/libstd/rt/unwind.rs
index e064663b9e7..659e787a9ff 100644
--- a/src/libstd/rt/unwind.rs
+++ b/src/libstd/rt/unwind.rs
@@ -494,6 +494,7 @@ pub extern fn rust_begin_unwind(msg: fmt::Arguments,
 /// on (e.g.) the inlining of other functions as possible), by moving
 /// the actual formatting into this shared place.
 #[inline(never)] #[cold]
+#[stable(since = "1.0.0", feature = "rust1")]
 pub fn begin_unwind_fmt(msg: fmt::Arguments, file_line: &(&'static str, uint)) -> ! {
     use fmt::Writer;
 
@@ -509,6 +510,7 @@ pub fn begin_unwind_fmt(msg: fmt::Arguments, file_line: &(&'static str, uint)) -
 
 /// This is the entry point of unwinding for panic!() and assert!().
 #[inline(never)] #[cold] // avoid code bloat at the call sites as much as possible
+#[stable(since = "1.0.0", feature = "rust1")]
 pub fn begin_unwind<M: Any + Send>(msg: M, file_line: &(&'static str, uint)) -> ! {
     // Note that this should be the only allocation performed in this code path.
     // Currently this means that panic!() on OOM will invoke this code path,