mod/chat - Normal method now support HTTP Keep-Alive

mod/chat - Normal method now support HTTP Keep-Alive

By using output buffering, we now support HTTP Keep-Alive, which means
that each client gets tightly bound to a single apache child - this means
that we get

 + lower resource usage on the webserver
 + _much_ lower resource usage on webserver and dbserver if pconnects are used
 + a good case for further caching (memcache/mmcache)

Using ab via localhost or fast LAN using keepalives is actually slower from the
client perspective -- still lighter on the server. Via slower links (DSL/modem)
the responses are faster.