1.5.2 update

This is an update for the soon to be released AG JS 1.5.2 lib.  

Also for the review of https://issues.jboss.org/browse/AGPUSH-856
It's not clear from the README itself where `mailEndpoint` comes from (I know you say people should open the code in an editor, but some of them simply won't, so consistency matters).

Following snippet is missing there:

````
// extract the endpoint object from the event:
mailEndpoint = event.target.result;
````

There is also `mailEndpoint` variable in the sample and then there figures `pushEndpoint` as its text description. 

Two options here:
* rename the variable to `pushEndpoint` in the sample and the text to stay aligned with the API docs
* but later in the text you do a comparison `message.pushEndpoint === mailEndpoint` so it make sense to leave the variable name