reset underscore prefix to functions variable

Author: jdeniau

lib/Elastica/Query/FunctionScore.php

@@ -30,7 +30,7 @@ class FunctionScore extends AbstractQuery
     const DECAY_EXPONENTIAL = 'exp';
     const DECAY_LINEAR = 'linear';
 
-    protected $functions = array();
+    protected $_functions = array();
 
     /**
      * Set the child query for this function_score query
@@ -69,7 +69,7 @@ public function addFunction($functionType, $functionParams, AbstractFilter $filt
         if ($weight !== null) {
             $function['weight'] = $weight;
         }
-        $this->functions[] = $function;
+        $this->_functions[] = $function;
         return $this;
     }
 
@@ -215,8 +215,8 @@ public function setScoreMode($mode)
      */
     public function toArray()
     {
-        if (sizeof($this->functions)) {
-            $this->setParam('functions', $this->functions);
+        if (sizeof($this->_functions)) {
+            $this->setParam('functions', $this->_functions);
         }
         return parent::toArray();
     }