improve error handling if connection to JS plugin update service is not possible

available-plugins.jsp offers "The list of available plugins has not yet been downloaded. Click here to download the list".
If I do so one or more times then I will find one 1 stack trace in STDERR, the web gui will display "Downloading .." and then "The list of available plugins has not yet been downloaded. Click here to download the list" again without any indication that an error did occur.

stack trace:
java.net.ConnectException: Connection refused: connect
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.PlainSocketImpl.doConnect(PlainSocketImpl.java:333)
at java.net.PlainSocketImpl.connectToAddress(PlainSocketImpl.java:195)
at java.net.PlainSocketImpl.connect(PlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:366)
at java.net.Socket.connect(Socket.java:507)
at java.net.Socket.connect(Socket.java:457)
at java.net.Socket.<init>(Socket.java:365)
at java.net.Socket.<init>(Socket.java:238)
at org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:79)
at org.apache.commons.httpclient.protocol.DefaultProtocolSocketFactory.createSocket(DefaultProtocolSocketFactory.java:121)
at org.apache.commons.httpclient.HttpConnection.open(HttpConnection.java:706)
at org.apache.commons.httpclient.HttpMethodDirector.executeWithRetry(HttpMethodDirector.java:386)
at org.apache.commons.httpclient.HttpMethodDirector.executeMethod(HttpMethodDirector.java:170)
at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:396)
at org.apache.commons.httpclient.HttpClient.executeMethod(HttpClient.java:324)
at org.jivesoftware.wildfire.update.UpdateManager.checkForServerUpdate(UpdateManager.java:192)
at org.jivesoftware.wildfire.update.PluginDownloadManager.updatePluginsList(PluginDownloadManager.java:70)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at uk.ltd.getahead.dwr.impl.ExecuteQuery.execute(ExecuteQuery.java:239)
at uk.ltd.getahead.dwr.impl.DefaultExecProcessor.handle(DefaultExecProcessor.java:48)
at uk.ltd.getahead.dwr.impl.DefaultProcessor.handle(DefaultProcessor.java:81)
at uk.ltd.getahead.dwr.AbstractDWRServlet.doPost(AbstractDWRServlet.java:162)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:616)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
at org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:428)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:830)
at com.opensymphony.module.sitemesh.filter.PageFilter.parsePage(PageFilter.java:118)
at com.opensymphony.module.sitemesh.filter.PageFilter.doFilter(PageFilter.java:52)
at org.mortbay.jetty.servlet.WebApplicationHandler$CachedChain.doFilter(WebApplicationHandler.java:821)
at org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:471)
at org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:568)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1530)
at org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:633)
at org.mortbay.http.HttpContext.handle(HttpContext.java:1482)
at org.mortbay.http.HttpServer.service(HttpServer.java:909)
at org.mortbay.http.HttpConnection.service(HttpConnection.java:816)
at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:982)
at org.mortbay.http.HttpConnection.handle(HttpConnection.java:833)
at org.mortbay.http.SocketListener.handleConnection(SocketListener.java:244)
at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357)
at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)