Change minimimum required PHP version to 5.3.23

- JSON_UNESCAPED_FLAGS is only available starting in 5.4.0; test for it before
  attempting to use it.

Author: weierophinney

composer.json

@@ -26,7 +26,7 @@
         }
     },
     "require": {
-        "php": ">=5.4.8",
+        "php": ">=5.3.23",
         "zendframework/zend-eventmanager": "~2.3-dev",
         "zendframework/zend-json": "~2.3-dev",
         "zendframework/zend-mvc": "~2.3-dev",

src/ZF/ApiProblem/ApiProblemResponse.php

@@ -13,8 +13,18 @@
  */
 class ApiProblemResponse extends Response
 {
+    /**
+     * @var ApiProblem
+     */
     protected $apiProblem;
 
+    /**
+     * Flags to use with json_encode 
+     * 
+     * @var int
+     */
+    protected $jsonFlags = 0;
+
     /**
      * @param ApiProblem $apiProblem
      */
@@ -23,6 +33,10 @@ public function __construct(ApiProblem $apiProblem)
         $this->apiProblem = $apiProblem;
         $this->setStatusCode($apiProblem->status);
         $this->setReasonPhrase($apiProblem->title);
+
+        if (defined('JSON_UNESCAPED_SLASHES')) {
+            $this->jsonFlags = constant('JSON_UNESCAPED_SLASHES');
+        }
     }
 
     /**
@@ -42,7 +56,7 @@ public function getApiProblem()
      */
     public function getContent()
     {
-        return json_encode($this->apiProblem->toArray(), JSON_UNESCAPED_SLASHES);
+        return json_encode($this->apiProblem->toArray(), $this->jsonFlags);
     }
 
     /**