Add autoderef tests for by-value trait objects.

Author: qnighy

src/test/run-pass/unsized-locals/by-value-trait-object-safety-withdefault.rs

@@ -24,4 +24,8 @@ impl Foo for A {}
 fn main() {
     let x = *(Box::new(A) as Box<dyn Foo>);
     assert_eq!(x.foo(), format!("hello"));
+
+    // I'm not sure whether we want this to work
+    let x = Box::new(A) as Box<dyn Foo>;
+    assert_eq!(x.foo(), format!("hello"));
 }

src/test/run-pass/unsized-locals/by-value-trait-object-safety.rs

@@ -26,4 +26,8 @@ impl Foo for A {
 fn main() {
     let x = *(Box::new(A) as Box<dyn Foo>);
     assert_eq!(x.foo(), format!("hello"));
+
+    // I'm not sure whether we want this to work
+    let x = Box::new(A) as Box<dyn Foo>;
+    assert_eq!(x.foo(), format!("hello"));
 }