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/main/java/rx/lang/jruby/JRubyAdaptor.java

@@ -84,7 +84,7 @@ public void testFilterViaGroovy() {
 
         @Test
         public void testLast() {
-            String script = "mockApiCall.getObservable().last().subscribe(lambda{|result| a.received(result)})";
+            String script = "mockApiCall.getObservable().takeLast(1).subscribe(lambda{|result| a.received(result)})";
             runGroovyScript(script);
             verify(assertion, times(1)).received("hello_1");
         }