auto merge of #5578 : erickt/rust/incoming, r=jbclements,erickt

Hey folks,

This patch series does some work on the json decoder, specifically with auto decoding of enums. Previously, we would take this code:

```
enum A {
    B,
    C(~str, uint)
}
```

and would encode a value of this enum to either `["B", []]` or `["C", ["D", 123]]`. I've changed this to `"B"` or `["C", "D", 123]`. This matches the style of the O'Caml json library [json-wheel](http://mjambon.com/json-wheel.html). I've added tests to make sure all this work.

In order to make this change, I added passing a `&[&str]` vec to `Decode::emit_enum_variant` so the json decoder can convert the name of a variant into it's position. I also changed the impl of `Encodable` for `Option<T>` to have the right upper casing.

I also did some work on the parser, which allows for `fn foo<T: ::cmp::Eq>() { ... }` statements (#5572), fixed the pretty printer properly expanding `debug!("...")` expressions, and removed `ast::expr_vstore_fixed`, which doesn't appear to be used anymore.

diff --cc src/librustc/middle/astencode.rs
Simple merge

diff --cc src/librustc/middle/liveness.rs
Simple merge

diff --cc src/librustc/middle/moves.rs
Simple merge

diff --cc src/librustc/middle/trans/expr.rs
Simple merge

diff --cc src/librustc/middle/ty.rs
Simple merge

diff --cc src/librustc/middle/typeck/check/mod.rs
Simple merge

diff --cc src/libstd/ebml.rs
Simple merge

diff --cc src/libsyntax/ast.rs
Simple merge

diff --cc src/libsyntax/fold.rs
Simple merge

diff --cc src/libsyntax/parse/parser.rs
Simple merge

diff --cc src/libsyntax/print/pprust.rs
Simple merge