librustc: Make overloaded operators with explicit self translate correctly

src/test/run-pass/operator-overloading-explicit-self.rs

@@ -0,0 +1,16 @@
+struct S {
+    x: int
+}
+
+impl S {
+    pure fn add(&self, other: &S) -> S {
+        S { x: self.x + other.x }
+    }
+}
+
+fn main() {
+    let mut s = S { x: 1 };
+    s += S { x: 2 };
+    assert s.x == 3;
+}
+