don't show errors about redirection status codes. Use the right channel.

bug 247490, r=mostafah

calendar/resources/content/calendarManager.js

@@ -670,11 +670,20 @@ calendarManager.prototype.getRemoteCalendarText = function calMan_getRemoteCalen
          if( typeof( result ) != "string" ) //for 1.7 compatibility
              result = String.fromCharCode.apply(this, result);
 
-         var ch = Channel.QueryInterface(Components.interfaces.nsIHttpChannel);
-         if (!ch.requestSucceeded) {
+         var ch;
+         try {
+           ch = loader.request.QueryInterface(Components.interfaces.nsIHttpChannel);
+         } catch(e) {
+         }
+         if (ch && !ch.requestSucceeded) {
            alert("Getting the calendar file failed.\nStatus code: "+ch.responseStatus+": "+ch.responseStatusText);
          }
 
+         else if (!Components.isSuccessCode(loader.request.status)) {
+           // XXX this should be made human-readable.
+           alert("Getting the calendar file failed.\nStatus code: 0x"+loader.request.status.toString(16));
+         }
+
          //check to make sure its actually a calendar file, if not return.
          else if( result.indexOf( "BEGIN:VCALENDAR" ) == -1 )
          {