Add clearScroll method

Client was missing the ability to explicitly clear a scroll.  It was
previously possible using the older "scroll=0m" method, but this commit
adds support for explicit clears via Delete.

src/Elasticsearch/Client.php

@@ -1068,6 +1068,35 @@ public function scroll($params = array())
     }
 
 
+    /**
+     * $params['scroll_id'] = (string) The scroll ID for scrolled search
+     *        ['scroll']    = (duration) Specify how long a consistent view of the index should be maintained for scrolled search
+     *        ['body']      = (string) The scroll ID for scrolled search
+     *
+     * @param $params array Associative array of parameters
+     *
+     * @return array
+     */
+    public function clearScroll($params = array())
+    {
+        $scrollID = $this->extractArgument($params, 'scroll_id');
+
+        $body = $this->extractArgument($params, 'body');
+
+        /** @var callback $endpointBuilder */
+        $endpointBuilder = $this->dicEndpoints;
+
+        /** @var \Elasticsearch\Endpoints\Scroll $endpoint */
+        $endpoint = $endpointBuilder('Scroll');
+        $endpoint->setScrollID($scrollID)
+                 ->setBody($body)
+                 ->setClearScroll(true);
+        $endpoint->setParams($params);
+        $response = $endpoint->performRequest();
+        return $response['data'];
+    }
+
+
     /**
      * $params['id']                = (string) Document ID (Required)
      *        ['index']             = (string) The name of the index (Required)

src/Elasticsearch/Endpoints/Scroll.php

@@ -25,6 +25,8 @@ class Scroll extends AbstractEndpoint
     // The scroll ID
     private $scroll_id;
 
+    private $clear = false;
+
 
     /**
      * @param array $body
@@ -44,6 +46,12 @@ public function setBody($body)
     }
 
 
+    public function setClearScroll($clear)
+    {
+        $this->clear = $clear;
+        return $this;
+    }
+
 
     /**
      * @param $scroll_id
@@ -94,6 +102,10 @@ protected function getParamWhitelist()
      */
     protected function getMethod()
     {
+        if ($this->clear == true) {
+            return 'DELETE';
+        }
+
         return 'GET';
     }
 }