Config FPC Placeholder Definition

This should go in cache.xml. See Boilerplate FPC No-Cache Container for a boilerplate container.

<config>
    <placeholders>
        <namespace_module>
            <block>namespace_module/something</block>
            <placeholder>NAMESPACE_MODULE_UNIQUE_STRING</placeholder>
            <container>Namespace_Module_Model_Pagecache_Container</container>
            <cache_lifetime>86400</cache_lifetime> <!-- never gets used -->
        </namespace_module>
    </placeholders>
</config>