Convert to interface to allow usage as lambda.

Author: dkocher

core/src/main/java/ch/cyberduck/core/threading/BackgroundExceptionCallable.java

@@ -19,7 +19,7 @@
 
 import java.util.concurrent.Callable;
 
-public abstract class BackgroundExceptionCallable<T> implements Callable<T> {
+public interface BackgroundExceptionCallable<T> extends Callable<T> {
     @Override
-    public abstract T call() throws BackgroundException;
+    T call() throws BackgroundException;
 }

s3/src/main/java/ch/cyberduck/core/s3/S3PathStyleFallbackAdapter.java

@@ -23,7 +23,7 @@
 import org.apache.logging.log4j.LogManager;
 import org.apache.logging.log4j.Logger;
 
-public class S3PathStyleFallbackAdapter<R> extends BackgroundExceptionCallable<R> {
+public class S3PathStyleFallbackAdapter<R> implements BackgroundExceptionCallable<R> {
     private static final Logger log = LogManager.getLogger(S3PathStyleFallbackAdapter.class);
 
     private final RequestEntityRestStorageService client;