[#2405] Porting kernel.terminate changes into the 2.1 branch

Author: weaverryan

book/internals.rst

@@ -361,6 +361,22 @@ The ``FrameworkBundle`` registers several listeners:
 
     Read more on the :ref:`kernel.response event <component-http-kernel-kernel-response>`.
 
+.. index::
+   single: Event; kernel.terminate
+
+``kernel.terminate`` Event
+..........................
+
+.. versionadded:: 2.1
+    The ``kernel.terminate`` event is new since Symfony 2.1.
+
+The purpose of this event is to perform "heavier" tasks after the response
+was already served to the client.
+
+.. seealso::
+
+    Read more on the :ref:`kernel.terminate event <component-http-kernel-kernel-terminate>`.
+
 .. index::
    single: Event; kernel.exception
 

components/http_kernel/introduction.rst

@@ -446,6 +446,8 @@ method, which sends the headers and prints the ``Response`` content.
     serializes the current user's information into the
     session so that it can be reloaded on the next request. 
 
+.. _component-http-kernel-kernel-terminate:
+
 8) The ``kernel.terminate`` event
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~