Add method to remove the pending request of the client

[thijsvdanker]

I was a little bit to trigger happy on #130 as the client in #130 is not available to me in this example #129

$this->setupFirstQuery();
try {
    $this->client->executeQuery();
} catch (Exception $e) {
   $this->client->clear();
    $this->setupSecondQuery();
    $this->client->executeQuery();
}

This merge request adds a removePendingRequest() method to the ClientRuntimeContext which is available to the code example above.
The result would be:

$this->setupFirstQuery();
try {
    $this->client->executeQuery();
} catch (Exception $e) {
   $this->client->removePendingRequest();
    $this->setupSecondQuery();
    $this->client->executeQuery();
}

I'm sorry for the confusion. The clear() method from #130 might not be that useful so we could consider removing it again...

[vgrem]

Hi @thijsvdanker,

First of all, much appreciated your contributions!
This was indeed an important issue and I like the idea and changes you proposed but i think we could improve it a bit.

Instead of introducing removePendingRequest and clear methods i propose the change which allows to manage request queue in automatic matter as the following example demonstrates:

   try{
        //lets try to load non-existent list to simulate the exception
        $listTitle = "Orders_" . rand(1,100000);
        $list = $context->getWeb()->getLists()->getByTitle($listTitle);
        $context->load($list);
        $context->executeQuery();
    }
    catch(Exception $e){
        //in case if previous request failed, the next request from a queue could be executed like this
        $user = $context->getWeb()->getCurrentUser();
        $context->load($user);
        $context->executeQuery();          
    }