make it compile in SBT & Eclipse with 2.9.2-SNAPSHOT

- there is one remaining bug, which makes it impossible to implement
  Function1[T, Boolean] from Java (I wonder if this will ever work,
  given that there is no equivalent type expressible in Java)
- hence create Function1 in Scala code, Java only prepares a Filter SAM
  which does not inherit from anything
- ugly (one more alloc) but the only way I see right now.

akka-actor-tests/src/test/java/akka/dispatch/JavaFutureTests.java

@@ -148,12 +148,12 @@ public class JavaFutureTests {
     final CountDownLatch latch = new CountDownLatch(1);
     Promise<String> cf = Futures.promise(system.dispatcher());
     Future<String> f = cf;
-    Future<String> r = f.filter(new Filter<String>() {
+    Future<String> r = f.filter(Filter.create(new Filter<String>() {
       public boolean filter(String r) {
         latch.countDown();
         return r.equals("foo");
       }
-    });
+    }));
 
     cf.success("foo");
     assertTrue(latch.await(5000, TimeUnit.MILLISECONDS));