Expressions with += are not correctly captured

Created by: benjreinhart

Attempting to capture an expression with +=, -=, *= or /= does not seem to get correctly captured.

Given the following macro:

macro t {
  rule {($body ... $last:expr)} => {
    function() {
        $body ...
        return $last 
    }
  }
}

This works ok:

var f = "string";
var f1 = t(f + "2");

But this does not:

var f = "string";
var f1 = t(f += "2");

var f = 10;
var f1 = t(f -= 2);

var f = 10;
var f1 = t(f *= 2);

var f = 10;
var f1 = t(f /= 2);

In all of those cases, it tries to expand to [lhs] [operator] return [rhs].

I realize this example is a bit contrived, but definitely still seems to be a bug.