Auto merge of #24177 - alexcrichton:rustdoc, r=aturon

This commit series starts out with more official test harness support for rustdoc tests, and then each commit afterwards adds a test (where appropriate). Each commit should also test and finish independently of all others (they're all pretty separable).

I've uploaded a [copy of the documentation](http://people.mozilla.org/~acrichton/doc/std/) generated after all these commits were applied, and a double check on issues being closed would be greatly appreciated! I'll also browse the docs a bit and make sure nothing regressed too horribly.

src/libcore/char.rs

@@ -139,6 +139,7 @@ pub fn from_digit(num: u32, radix: u32) -> Option<char> {
 // NB: the stabilization and documentation for this trait is in
 // unicode/char.rs, not here
 #[allow(missing_docs)] // docs in libunicode/u_char.rs
+#[doc(hidden)]
 pub trait CharExt {
     fn is_digit(self, radix: u32) -> bool;
     fn to_digit(self, radix: u32) -> Option<u32>;

src/libcore/macros.rs

@@ -229,7 +229,6 @@ macro_rules! writeln {
 /// Iterators:
 ///
 /// ```
-/// # #![feature(core)]
 /// fn divide_by_three(x: u32) -> u32 { // one of the poorest implementations of x/3
 ///     for i in 0.. {
 ///         if 3*i < i { panic!("u32 overflow"); }

src/libcore/num/mod.rs

@@ -2490,6 +2490,7 @@ pub enum FpCategory {
 //               `unused_self`. Removing it requires #8888 to be fixed.
 #[unstable(feature = "core",
            reason = "distribution of methods between core/std is unclear")]
+#[doc(hidden)]
 pub trait Float
     : Copy + Clone
     + NumCast

src/libcore/ptr.rs

@@ -89,6 +89,7 @@
 //! of unsafe pointers in Rust.
 
 #![stable(feature = "rust1", since = "1.0.0")]
+#![doc(primitive = "pointer")]
 
 use mem;
 use clone::Clone;

src/libcore/slice.rs

@@ -63,6 +63,7 @@ use raw::Slice as RawSlice;
 
 /// Extension methods for slices.
 #[allow(missing_docs)] // docs in libcollections
+#[doc(hidden)]
 pub trait SliceExt {
     type Item;
 

src/libcore/str/mod.rs

@@ -1496,6 +1496,7 @@ impl<'a, S: ?Sized> Str for &'a S where S: Str {
 
 /// Methods for string slices
 #[allow(missing_docs)]
+#[doc(hidden)]
 pub trait StrExt {
     // NB there are no docs here are they're all located on the StrExt trait in
     // libcollections, not here.