INT-3175 Add Caution About Apache HTTP Client

JIRA: https://jira.springsource.org/browse/INT-3175

src/reference/docbook/http.xml

@@ -619,7 +619,7 @@ By default the HTTP request will be generated using an instance of <classname>Si
    </para>
    <para>
        <classname><ulink url="http://static.springsource.org/spring/docs/current/javadoc-api/org/springframework/http/client/HttpComponentsClientHttpRequestFactory.html">HttpComponentsClientHttpRequestFactory</ulink></classname>
-       - Uses <ulink url="http://hc.apache.org/httpcomponents-client-ga/httpclient/">Apache HttpComponents HttpClient</ulink> (Since Spring 3.1)
+       - Uses <ulink url="http://hc.apache.org/httpcomponents-client-ga/">Apache HttpComponents HttpClient</ulink> (Since Spring 3.1)
    </para>
    <para>
        <classname><ulink url="http://static.springsource.org/spring/docs/current/javadoc-api/org/springframework/http/client/CommonsClientHttpRequestFactory.html">ClientHttpRequestFactory</ulink></classname>
@@ -652,6 +652,13 @@ By default the HTTP request will be generated using an instance of <classname>Si
        </para>
    </note>
 
+   <important>
+       When using the <emphasis>Apache HttpComponents HttpClient</emphasis> with a Pooling Connection Manager, be aware that, by
+       default, the connection manager will create no more than 2 concurrent connections per given route and no more than 20 connections
+       in total. For many real-world applications these limits may prove too constraining. Refer to the Apache documentation
+       (link above) for information about configuring this important component.
+   </important>
+
    <para>
        Here is an example of how to configure an <emphasis>HTTP Outbound Gateway</emphasis>
        using a <classname>SimpleClientHttpRequestFactory</classname>, configured