setTouchPriority doesn't work due to a bug in CCTouchDispatcher

The bug was introduced in this fix: http://cocos2d-x.org/issues/752
I created an issue in issue tracker too: http://www.cocos2d-x.org/issues/4317
This is my first pull request, I am not sure if the fix is correct, but the issue certainly exists. The problem is that CCLayer's setTouchPriority method sometimes has no effect. The fix was created by wondeful18.

Test case:

I created a Layer, which has a sole purpose to block ("swallow";) touches, and this feature can be turned on and off.
The class is very basic, if it receives the touch it always swallows it:

`bool BlockingLayer::init(){

// Super init.
if ( !CCLayer::init() )
{
return false;
}

setTouchEnabled(true);
setTouchMode(kCCTouchesOneByOne);
setTouchPriority(INT_MAX);

return true;
}

bool BlockingLayer::ccTouchBegan(CCTouch *pTouch, CCEvent *pEvent)
{
CCLOG("BlockingLayer swallowed touch!");
return true;
}

So by default it has a really bad priority, it receives touches if no other class claimed it. But in the scene where I am using this layer I would like to set it to a different priority when certain events occur:

bool MyScene::init(int unitNumber, CCString* path){
// Super init.
...
blockingLayer = BlockingLayer::create();
this->addChild(blockingLayer);

return true;
}

bool MyScene::ccTouchBegan(CCTouch *pTouch, CCEvent *pEvent){
blockingLayer->setTouchPriority(INTMIN);
}`

Now the layer should have the best priority possible, so it should swallow all touches. But it does not, it's behaviour does not change.
I see its registerWithTouchDispatcher() called and the m_nTouchPriority changed correctly. BUT the layer's behaviour is unchanged.