[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/test/compile-fail/coherence-default-trait-impl.rs

@@ -13,7 +13,7 @@
 trait MyTrait { fn foo() {} }
 
 impl MyTrait for .. {}
-//~^ ERROR redundant default implementations of trait `MyTrait`
+//~^ ERROR redundant auto implementations of trait `MyTrait`
 
 impl MyTrait for .. {}
 

src/test/compile-fail/feature-gate-optin-builtin-traits.rs

@@ -18,7 +18,7 @@ trait DummyTrait {
 }
 
 impl DummyTrait for .. {}
-//~^ ERROR default trait implementations are experimental and possibly buggy
+//~^ ERROR auto trait implementations are experimental and possibly buggy
 
 impl !DummyTrait for DummyStruct {}
 //~^ ERROR negative trait bounds are not yet fully implemented; use marker types for now

src/test/compile-fail/specialization/defaultimpl/specialization-no-default-trait-implementations.rs

@@ -14,6 +14,6 @@
 trait Foo {}
 
 default impl Foo for .. {}
-//~^ ERROR `default impl` is not allowed for default trait implementations
+//~^ ERROR `default impl` is not allowed for auto trait implementations
 
 fn main() {}

src/test/compile-fail/syntaxt-default-trait-impls.rs

@@ -10,9 +10,9 @@
 
 #![feature(optin_builtin_traits)]
 
-trait MyDefaultImpl {}
+trait MyAutoImpl {}
 
-impl<T> MyDefaultImpl for .. {}
-//~^ ERROR default trait implementations are not allowed to have generics
+impl<T> MyAutoImpl for .. {}
+//~^ ERROR auto trait implementations are not allowed to have generics
 
 fn main() {}

src/test/incremental/hashes/trait_defs.rs

@@ -249,7 +249,7 @@ trait TraitChangeMethodParametersOrder {
 
 // Add default implementation to method -------------------------------------------
 #[cfg(cfail1)]
-trait TraitAddMethodDefaultImplementation {
+trait TraitAddMethodAutoImplementation {
     fn method();
 }
 
@@ -258,7 +258,7 @@ trait TraitAddMethodDefaultImplementation {
 #[rustc_clean(label="Hir", cfg="cfail3")]
 #[rustc_metadata_clean(cfg="cfail2")]
 #[rustc_metadata_clean(cfg="cfail3")]
-trait TraitAddMethodDefaultImplementation {
+trait TraitAddMethodAutoImplementation {
     #[rustc_dirty(label="Hir", cfg="cfail2")]
     #[rustc_clean(label="Hir", cfg="cfail3")]
     #[rustc_metadata_dirty(cfg="cfail2")]