std: Rename Show/String to Debug/Display

This commit is an implementation of [RFC 565][rfc] which is a stabilization of
the `std::fmt` module and the implementations of various formatting traits.
Specifically, the following changes were performed:

[rfc]: https://github.com/rust-lang/rfcs/blob/master/text/0565-show-string-guidelines.md

* The `Show` trait is now deprecated, it was renamed to `Debug`
* The `String` trait is now deprecated, it was renamed to `Display`
* Many `Debug` and `Display` implementations were audited in accordance with the
  RFC and audited implementations now have the `#[stable]` attribute
  * Integers and floats no longer print a suffix
  * Smart pointers no longer print details that they are a smart pointer
  * Paths with `Debug` are now quoted and escape characters
* The `unwrap` methods on `Result` now require `Display` instead of `Debug`
* The `Error` trait no longer has a `detail` method and now requires that
  `Display` must be implemented. With the loss of `String`, this has moved into
  libcore.
* `impl<E: Error> FromError<E> for Box<Error>` now exists
* `derive(Show)` has been renamed to `derive(Debug)`. This is not currently
  warned about due to warnings being emitted on stage1+

While backwards compatibility is attempted to be maintained with a blanket
implementation of `Display` for the old `String` trait (and the same for
`Show`/`Debug`) this is still a breaking change due to primitives no longer
implementing `String` as well as modifications such as `unwrap` and the `Error`
trait. Most code is fairly straightforward to update with a rename or tweaks of
method calls.

[breaking-change]
Closes #21436

src/libstd/sync/mpsc/mod.rs

@@ -393,7 +393,7 @@ impl<T> !marker::Sync for SyncSender<T> {}
 /// A `send` operation can only fail if the receiving end of a channel is
 /// disconnected, implying that the data could never be received. The error
 /// contains the data being sent as a payload so it can be recovered.
-#[derive(PartialEq, Eq)]
+#[derive(PartialEq, Eq, Show)]
 #[stable]
 pub struct SendError<T>(pub T);
 
@@ -401,13 +401,13 @@ pub struct SendError<T>(pub T);
 ///
 /// The `recv` operation can only fail if the sending half of a channel is
 /// disconnected, implying that no further messages will ever be received.
-#[derive(PartialEq, Eq, Clone, Copy)]
+#[derive(PartialEq, Eq, Clone, Copy, Show)]
 #[stable]
 pub struct RecvError;
 
 /// This enumeration is the list of the possible reasons that try_recv could not
 /// return data when called.
-#[derive(PartialEq, Clone, Copy)]
+#[derive(PartialEq, Clone, Copy, Show)]
 #[stable]
 pub enum TryRecvError {
     /// This channel is currently empty, but the sender(s) have not yet
@@ -423,7 +423,7 @@ pub enum TryRecvError {
 
 /// This enumeration is the list of the possible error outcomes for the
 /// `SyncSender::try_send` method.
-#[derive(PartialEq, Clone)]
+#[derive(PartialEq, Clone, Show)]
 #[stable]
 pub enum TrySendError<T> {
     /// The data could not be sent on the channel because it would require that
@@ -998,13 +998,15 @@ unsafe impl<T:Send> Send for RacyCell<T> { }
 
 unsafe impl<T> Sync for RacyCell<T> { } // Oh dear
 
-impl<T> fmt::Show for SendError<T> {
+#[stable]
+impl<T> fmt::Display for SendError<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         "sending on a closed channel".fmt(f)
     }
 }
 
-impl<T> fmt::Show for TrySendError<T> {
+#[stable]
+impl<T> fmt::Display for TrySendError<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             TrySendError::Full(..) => {
@@ -1017,13 +1019,15 @@ impl<T> fmt::Show for TrySendError<T> {
     }
 }
 
-impl fmt::Show for RecvError {
+#[stable]
+impl fmt::Display for RecvError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         "receiving on a closed channel".fmt(f)
     }
 }
 
-impl fmt::Show for TryRecvError {
+#[stable]
+impl fmt::Display for TryRecvError {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match *self {
             TryRecvError::Empty => {