Move zend_object handler to the end

In php7 the zend_object handler structure is inlined (is no longer a pointer,
but rather variable sized depending on various things, so it needs to be at the
end of the container class.

This is mentioned in the extensive /s upgrading documentation from Zend

See "custom objects":
https://wiki.php.net/phpng-upgrading

In addition I believe that the zend library now takes care of freeing the overall
structure, so that shouldn't be done anymore if running php >= 7.0.0.

cluster_library.h

@@ -173,9 +173,6 @@ typedef struct clusterFoldItem clusterFoldItem;
 
 /* RedisCluster implementation structure */
 typedef struct redisCluster {
-    /* Object reference for Zend */
-    zend_object std;
-
     /* Timeout and read timeout (for normal operations) */
     double timeout;
     double read_timeout;
@@ -244,6 +241,9 @@ typedef struct redisCluster {
     int                redir_host_len;
     unsigned short     redir_slot;
     unsigned short     redir_port;
+
+    /* Zend object handler */
+    zend_object std;
 } redisCluster;
 
 /* RedisCluster response processing callback */

redis_cluster.c

@@ -331,14 +331,20 @@ create_cluster_context(zend_class_entry *class_type TSRMLS_DC) {
 #else
 	object_properties_init(&cluster->std, class_type);
 	memcpy(&RedisCluster_handlers, zend_get_std_object_handlers(), sizeof(RedisCluster_handlers));
-	RedisCluster_handlers.free_obj = free_cluster_context;
+	RedisCluster_handlers.offset = XtOffsetOf(redisCluster, std);
+    RedisCluster_handlers.free_obj = free_cluster_context;
 
 	cluster->std.handlers = &RedisCluster_handlers;
 
 	return &cluster->std;
 #endif
 }
 
+/* Helper to retrieve the redisCluster object from the zend_object member */
+static redisCluster *getClusterObject(zend_object *object) {
+    return (redisCluster*)((char*)(object) - XtOffsetOf(redisCluster, std));
+}
+
 /* Free redisCluster context */
 void
 #if (PHP_MAJOR_VERSION < 7)
@@ -347,10 +353,7 @@ free_cluster_context(void *object TSRMLS_DC)
 free_cluster_context(zend_object *object)
 #endif
 {
-    redisCluster *cluster;
-
-    // Grab context
-    cluster = (redisCluster*)object;
+    redisCluster *cluster = getClusterObject(object);
 
     // Free any allocated prefix, as well as the struct
     if(cluster->flags->prefix) efree(cluster->flags->prefix);
@@ -366,8 +369,11 @@ free_cluster_context(zend_object *object)
 
     if(cluster->err) efree(cluster->err);
 
-    // Finally, free the redisCluster structure itself
+    zend_object_std_dtor(&cluster->std TSRMLS_CC);
+
+#if (PHP_MAJOR_VERSION < 7)
     efree(cluster);
+#endif
 }
 
 /* Attempt to connect to a Redis cluster provided seeds and timeout options */