fixes #189: use dotted member access when --screw-ie8 option given

test/compress/properties.js

@@ -23,3 +23,18 @@ dot_properties: {
         a["if"] = "if";
     }
 }
+
+dot_properties_es5: {
+    options = {
+        properties: true,
+        screw_ie8: true
+    };
+    input: {
+        a["foo"] = "bar";
+        a["if"] = "if";
+    }
+    expect: {
+        a.foo = "bar";
+        a.if = "if";
+    }
+}