serialize: Use assoc types + less old_orphan_check

This commit moves the libserialize crate (and will force the hand of the
rustc-serialize crate) to not require the `old_orphan_check` feature gate as
well as using associated types wherever possible. Concretely, the following
changes were made:

* The error type of `Encoder` and `Decoder` is now an associated type, meaning
  that these traits have no type parameters.

* The `Encoder` and `Decoder` type parameters on the `Encodable` and `Decodable`
  traits have moved to the corresponding method of the trait. This movement
  alleviates the dependency on `old_orphan_check` but implies that
  implementations can no longer be specialized for the type of encoder/decoder
  being implemented.

Due to the trait definitions changing, this is a:

[breaking-change]

1 files changed, 17 insertions, 0 deletions

diff --git a/src/libsyntax/parse/token.rs b/src/libsyntax/parse/token.rs
index 4bfcc94a083..b7e89b32b70 100644
--- a/src/libsyntax/parse/token.rs
+++ b/src/libsyntax/parse/token.rs
@@ -653,6 +653,7 @@ impl<'a> PartialEq<InternedString > for &'a str {
     }
 }
 
+#[cfg(stage0)]
 impl<D:Decoder<E>, E> Decodable<D, E> for InternedString {
     fn decode(d: &mut D) -> Result<InternedString, E> {
         Ok(get_name(get_ident_interner().intern(
@@ -660,12 +661,28 @@ impl<D:Decoder<E>, E> Decodable<D, E> for InternedString {
     }
 }
 
+#[cfg(not(stage0))]
+impl Decodable for InternedString {
+    fn decode<D: Decoder>(d: &mut D) -> Result<InternedString, D::Error> {
+        Ok(get_name(get_ident_interner().intern(
+                    try!(d.read_str())[])))
+    }
+}
+
+#[cfg(stage0)]
 impl<S:Encoder<E>, E> Encodable<S, E> for InternedString {
     fn encode(&self, s: &mut S) -> Result<(), E> {
         s.emit_str(self.string[])
     }
 }
 
+#[cfg(not(stage0))]
+impl Encodable for InternedString {
+    fn encode<S: Encoder>(&self, s: &mut S) -> Result<(), S::Error> {
+        s.emit_str(self.string[])
+    }
+}
+
 /// Returns the string contents of a name, using the task-local interner.
 #[inline]
 pub fn get_name(name: ast::Name) -> InternedString {