[Syntax Breaking] Rename DefaultImpl to AutoImpl

DefaultImpl is a highly confusing name for what we now call auto impls,
as in `impl Send for ..`. The name auto impl is not formally decided
but for sanity anything is better than `DefaultImpl` which refers
neither to `default impl` nor to `impl Default`.

src/librustdoc/clean/inline.rs

@@ -292,10 +292,10 @@ pub fn build_impl(cx: &DocContext, did: DefId, ret: &mut Vec<clean::Item>) {
         }
     }
 
-    // If this is a defaulted impl, then bail out early here
-    if tcx.is_default_impl(did) {
+    // If this is an auto impl, then bail out early here
+    if tcx.is_auto_impl(did) {
         return ret.push(clean::Item {
-            inner: clean::DefaultImplItem(clean::DefaultImpl {
+            inner: clean::AutoImplItem(clean::AutoImpl {
                 // FIXME: this should be decoded
                 unsafety: hir::Unsafety::Normal,
                 trait_: match associated_trait.as_ref().unwrap().clean(cx) {

src/librustdoc/clean/mod.rs

@@ -425,7 +425,7 @@ pub enum ItemEnum {
     PrimitiveItem(PrimitiveType),
     AssociatedConstItem(Type, Option<String>),
     AssociatedTypeItem(Vec<TyParamBound>, Option<Type>),
-    DefaultImplItem(DefaultImpl),
+    AutoImplItem(AutoImpl),
     /// An item that has been stripped by a rustdoc pass
     StrippedItem(Box<ItemEnum>),
 }
@@ -2733,12 +2733,12 @@ fn build_deref_target_impls(cx: &DocContext,
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
-pub struct DefaultImpl {
+pub struct AutoImpl {
     pub unsafety: hir::Unsafety,
     pub trait_: Type,
 }
 
-impl Clean<Item> for doctree::DefaultImpl {
+impl Clean<Item> for doctree::AutoImpl {
     fn clean(&self, cx: &DocContext) -> Item {
         Item {
             name: None,
@@ -2748,7 +2748,7 @@ impl Clean<Item> for doctree::DefaultImpl {
             visibility: Some(Public),
             stability: None,
             deprecation: None,
-            inner: DefaultImplItem(DefaultImpl {
+            inner: AutoImplItem(AutoImpl {
                 unsafety: self.unsafety,
                 trait_: self.trait_.clean(cx),
             }),