rollup merge of #20033: alexcrichton/deprecate-serialise

This commit completes the deprecation story for the in-tree serialization
library. The compiler will now emit a warning whenever it encounters
`deriving(Encodable)` or `deriving(Decodable)`, and the library itself is now
marked `#[unstable]` for when feature staging is enabled.

All users of serialization can migrate to the `rustc-serialize` crate on
crates.io which provides the exact same interface as the libserialize library
in-tree. The new deriving modes are named `RustcEncodable` and `RustcDecodable`
and require `extern crate "rustc-serialize" as rustc_serialize` at the crate
root in order to expand correctly.

To migrate all crates, add the following to your `Cargo.toml`:

    [dependencies]
    rustc-serialize = "0.1.1"

And then add the following to your crate root:

    extern crate "rustc-serialize" as rustc_serialize;

Finally, rename `Encodable` and `Decodable` deriving modes to `RustcEncodable`
and `RustcDecodable`.

[breaking-change]

src/libsyntax/codemap.rs

@@ -92,7 +92,7 @@ pub struct Span {
 
 pub const DUMMY_SP: Span = Span { lo: BytePos(0), hi: BytePos(0), expn_id: NO_EXPANSION };
 
-#[deriving(Clone, Copy, PartialEq, Eq, Encodable, Decodable, Hash, Show)]
+#[deriving(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Show, Copy)]
 pub struct Spanned<T> {
     pub node: T,
     pub span: Span,
@@ -218,7 +218,7 @@ pub struct ExpnInfo {
     pub callee: NameAndSpan
 }
 
-#[deriving(Copy, PartialEq, Eq, Clone, Show, Hash, Encodable, Decodable)]
+#[deriving(PartialEq, Eq, Clone, Show, Hash, RustcEncodable, RustcDecodable, Copy)]
 pub struct ExpnId(u32);
 
 pub const NO_EXPANSION: ExpnId = ExpnId(-1);