caolan/async — pull request #512 by i3fox (2014-04-16 09:39:37+00:00)
Title: async.queue pause/resume concurrency problem

In the async.queue I found an issue related to restart after a pause (resume) and I try to fix.
It's not simple to explain, please follow these steps:
1) for concurrency tasks are in execution
2) I pause the queue and wait for the execution of tasks finishes
3) I resume queue
4) Queue restarts but concurrency does not work: only one task is running.

Example of problem:

```javascript
var async = require("async");
var q = async.queue(function (task, callback) {
console.log('hello ' + task.name);
setTimeout(function() {
callback();
}, 2000);
}, 5);

q.pause();
q.push({name: '1'});
q.push({name: '2'});
q.push({name: '3'});
q.push({name: '4'});
q.push({name: '5'});
q.push({name: '6'});
q.push({name: '7'});
q.push({name: '8'});
q.push({name: '9'});
q.push({name: '10'});

setTimeout(function () {
q.resume();
}, 2500);
```