fix comment-attachment issue (#638)

The issue in brief: Within an object literal, if a standalone comment was followed by a commented symbol, the symbol's comment would not be attached correctly.

The fix essentially reverts the changes for #565, which are no longer needed thanks to 50cd99fa2fca753fcf7c9ec3ecf70afd47168e94.

The fix also corrects the order in which we walk a MemberExpression's child nodes. Without this correction, comments would not be attached correctly inside CallExpression nodes.