Fix broken addon browser.

Download to a valid location.  Stop silently failing, show errors to used.

Change-Id: If28e35e2e3dd7f31dd3099349ec8400095edb9af
Fixes-Issue: CLIENT-393
Reviewed-on: http://gerrit.dmdirc.com/2615
Automatic-Compile: DMDirc Build Manager
Reviewed-by: Shane Mc Cormack <shane@dmdirc.com>

src/com/dmdirc/addons/ui_swing/components/addonbrowser/InstallWorker.java

     protected String doInBackground() {
         try {
             final File file = new File(controller.getIdentityManager().getConfigDir(),
-                    "." + info.getDownload());
+                    "." + info.getId());
             Downloader.downloadPage("http://addons.dmdirc.com/addondownload/"
                     + info.getDownload(), file.getAbsolutePath());
 
     /** {@inheritDoc} */
     @Override
     protected void done() {
-        if (!isCancelled()) {
-            installer.finished("");
-            return;
-        }
         String message = "";
         try {
             message = get();