Fix issues with removing listeners from the queue

[russelldavis]

After switching to the next branch I discovered several issues introduced by #280:

• It was passing index instead of queueIndex to listenerQueue.splice. In addition to being the wrong index, this can put listenerQueue into a really weird/bad state when index is not divisible by 4 (since listenerQueue uses chunks of 4 items per listener).
• It was only removing the first listener it found in the queue, so it wouldn't work properly if the same listener was in the queue multiple times (e.g., when calling set on the same store multiple times inside a listener)
• It was removing items from the front of the queue, even if those items had already been processed. This would cause the next iteration of the queue processing loop to skip unprocessed items (because everything in the array gets shifted when calling splice)
• It was searching all items of listenerQueue for listener, but as mentioned above, only every 4th item is a valid position to search in. This meant that if a listener function was set as the value of a store, it would be incorrectly found as a listener, and listenerQueue would end up in a bad state. This is an unlikely scenario to happen in the real world, but easy enough to fix.

I added tests for all of those and fixed the issues.

cc @gismya

[gismya]

A superior solution. While the first issue was an embarrassing typo, I didn't consider the other issues and went for an overly simplistic solution. I love the clarity of the tests.

[ai]

Thanks!