VEND-8: Backport performance fix RF-10035 Richfaces creates too many DocumentBuilder

Backport fix from SP4 files:

    http://anonsvn.jboss.org/repos/richfaces/tags/3.3.1.SP4/framework/impl/src/main/java/org/ajax4jsf/util/DocumentBuilderPool.java
    http://anonsvn.jboss.org/repos/richfaces/tags/3.3.1.SP4/framework/impl/src/main/java/org/ajax4jsf/context/ResponseWriterContentHandler.java