Stack overflow in IE 11 when publish called on channel with many pending unsubscribes

[audreyality]

Steps to reproduce:

1. Download postal-overflow.zip
2. Unpack into a directory
3. Load in IE 11
4. Accept remote ActiveX (The warning comes up because it's loading JavaScript from disk)
5. Click "Go" button

The text "Out of stack space" should appear next to the "Error: " label.

Minimal example:

var testChannel = postal.channel("test_channel");

for(var i = 0; i < 745; i++) {
    var sub = testChannel.subscribe("whatevs", function(){ this.unsubscribe(); });
    sub.context(sub);
}

testChannel.publish("whatevs");

It looks like stack space is exhausted due to recursion among postal.unsubscribe, postal.publish, and clearUnSubQueue. postal.unsubscribe publishes the system removed message on line 655. postal.publish invokes clearUnSubQueue on line 550 because the system-level publish is concluding. clearUnSubQueue calls postal.unsubscribe on line 392 because there are unsubscriptions remaining in unSubQueue.

It appears that I could end the recursion by setting _config.enableSystemMessages to false. Nothing within posal.js subscribes to these messages, and I'm not using any plugins at this time. Is this an appropriate workaround?

My local tests (IE 11 on Windows 10) started exhibiting the error after 745 unsubscriptions are added to the queue.