fixes #52, fields shadowing getters/setters or other fields

test/codegen/expect/opassign.js

Index: test/codegen/expect/opassign.js
diff --git a/test/codegen/expect/opassign.js b/test/codegen/expect/opassign.js
index 52ca848086e9c69146fd2514640f9b024eb65184..28666815c60cde1b3f3fb99cc69b6bd62c2c73e2 100644
--- a/test/codegen/expect/opassign.js
+++ b/test/codegen/expect/opassign.js
@@ -18,9 +18,16 @@ var opassign;
       return exports._foo;
     }
   });
+  let x = Symbol('x');
   class Foo extends core.Object {
     Foo() {
-      this.x = 100;
+      this[x] = 100;
+    }
+    get x() {
+      return this[x];
+    }
+    set x(value) {
+      this[x] = value;
     }
   }
   // Function main: () → dynamic