Switch to purely namespaced enums

This breaks code that referred to variant names in the same namespace as
their enum. Reexport the variants in the old location or alter code to
refer to the new locations:

```
pub enum Foo {
    A,
    B
}

fn main() {
    let a = A;
}
```
=>
```
pub use self::Foo::{A, B};

pub enum Foo {
    A,
    B
}

fn main() {
    let a = A;
}
```
or
```
pub enum Foo {
    A,
    B
}

fn main() {
    let a = Foo::A;
}
```

[breaking-change]

src/librustdoc/clean/mod.rs

@@ -11,6 +11,22 @@
 //! This module contains the "cleaned" pieces of the AST, and the functions
 //! that clean them.
 
+pub use self::ImplMethod::*;
+pub use self::Type::*;
+pub use self::PrimitiveType::*;
+pub use self::TypeKind::*;
+pub use self::StructField::*;
+pub use self::VariantKind::*;
+pub use self::Mutability::*;
+pub use self::ViewItemInner::*;
+pub use self::ViewPath::*;
+pub use self::ItemEnum::*;
+pub use self::Attribute::*;
+pub use self::TyParamBound::*;
+pub use self::SelfTy::*;
+pub use self::FunctionRetTy::*;
+pub use self::TraitMethod::*;
+
 use syntax;
 use syntax::ast;
 use syntax::ast_util;
@@ -35,6 +51,8 @@ use rustc::middle::stability;
 
 use std::rc::Rc;
 use std::u32;
+use std::str::Str as StrTrait; // Conflicts with Str variant
+use std::char::Char as CharTrait; // Conflicts with Char variant
 
 use core::DocContext;
 use doctree;