Convert 'last' from non-blocking to blocking to match Rx.Net

See ReactiveX/RxJava#57 (comment) for background.

NOTE: This is a breaking change thus we are bumping the version from 0.5.x to 0.6.x

Manual merge of branch 'last' of git://github.com/mairbek/RxJava into issue-57-last

Conflicts:
	rxjava-core/src/main/java/rx/Observable.java

src/test/groovy/rx/lang/groovy/ObservableTests.groovy

@@ -30,6 +30,7 @@ import rx.Notification;
 import rx.Observable;
 import rx.Observer;
 import rx.Subscription;
+import rx.subscriptions.Subscriptions;
 import rx.util.functions.Func1;
 
 def class ObservableTests {
@@ -61,8 +62,12 @@ def class ObservableTests {
 
     @Test
     public void testLast() {
-        new TestFactory().getObservable().last().subscribe({ result -> a.received(result)});
-        verify(a, times(1)).received("hello_1");
+        assertEquals("three", Observable.toObservable("one", "two", "three").last())
+    }
+
+    @Test
+    public void testLastWithPredicate() {
+        assertEquals("two", Observable.toObservable("one", "two", "three").last({ x -> x.length() == 3}))
     }
 
     @Test
@@ -175,6 +180,12 @@ def class ObservableTests {
         verify(a, times(0)).received(3);
     }
 
+    @Test
+    public void testTakeLast() {   
+        new TestFactory().getObservable().takeLast(1).subscribe({ result -> a.received(result)});
+        verify(a, times(1)).received("hello_1");
+    }
+
     @Test
     public void testTakeWhileViaGroovy() {
         Observable.takeWhile(Observable.toObservable(1, 2, 3), { x -> x < 3}).subscribe({ result -> a.received(result)});
@@ -280,7 +291,7 @@ def class ObservableTests {
                     observer.onCompleted();
                 }
             }).start();
-            return Observable.noOpSubscription();
+            return Subscriptions.empty();
         }
     }