Make NewThreadScheduler create Daemon threads

This matches the behavior of Schedulers.COMPUTATION_EXECUTOR and Schedulers.IO_EXECUTOR.

See https://groups.google.com/forum/#!topic/rxjava/Qe1qi0aHtnE and #431 (comment)

Author: benjchristensen

rxjava-core/src/main/java/rx/schedulers/NewThreadScheduler.java

@@ -52,7 +52,9 @@ private EventLoopScheduler() {
 
                 @Override
                 public Thread newThread(Runnable r) {
-                    return new Thread(r, "RxNewThreadScheduler-" + count.incrementAndGet());
+                    Thread t = new Thread(r, "RxNewThreadScheduler-" + count.incrementAndGet());
+                    t.setDaemon(true);
+                    return t;
                 }
             });
         }