Don't let browsers cache job directory files for 10 minutes (#782)

Restlet's Directory gives every file an Expires header 10 minutes in the
future. Job files (logs, reports, crawler-beans.cxml) change constantly, so
browsers could show stale copies. Worst case, the config editor loads a
cached crawler-beans.cxml and saving it silently reverts newer changes.

Clear the expiration date and send Cache-Control: no-cache instead, so
browsers revalidate against Last-Modified on each use.

engine/src/main/java/org/archive/crawler/restlet/EnhDirectory.java

@@ -29,6 +29,7 @@ import org.restlet.Context;
 import org.restlet.data.Reference;
 import org.restlet.Request;
 import org.restlet.Response;
+import org.restlet.data.CacheDirective;
 import org.restlet.data.Status;
 import org.restlet.resource.Directory;
 import org.restlet.resource.ServerResource;
@@ -72,6 +73,14 @@ public abstract class EnhDirectory extends Directory {
             if (response.getStatus() == Status.SUCCESS_NO_CONTENT) {
                 response.setStatus(Status.SUCCESS_OK);
             }
+
+            // Job files (logs, reports, configs) change constantly, so replace Restlet's default
+            // 10 minute expiry with revalidation against Last-Modified. Otherwise the config editor
+            // can load a stale copy and saving it silently reverts newer changes.
+            if (response.getEntity() != null) {
+                response.getEntity().setExpirationDate(null);
+            }
+            response.getCacheDirectives().add(CacheDirective.noCache());
         }
     }