Add manual reporting of changes to the Darwin adapter

lib/listen/adapters/darwin.rb

@@ -25,13 +25,14 @@ def start(blocking = true)
         end
 
         @worker_thread = Thread.new { @worker.run }
-        @poll_thread   = Thread.new { poll_changed_dirs }
 
         # The FSEvent worker needs sometime to startup. Turnstiles can't
         # be used to wait for it as it runs in a loop.
         # TODO: Find a better way to block until the worker starts.
-        sleep @latency
-        @poll_thread.join if blocking
+        sleep 0.1
+
+        @poll_thread = Thread.new { poll_changed_dirs } if @report_changes
+        @worker_thread.join if blocking
       end
 
       # Stops the adapter.
@@ -43,8 +44,8 @@ def stop
         end
 
         @worker.stop
-        Thread.kill(@worker_thread) if @worker_thread
-        @poll_thread.join
+        @worker_thread.join if @worker_thread
+        @poll_thread.join if @poll_thread
       end
 
       # Checks if the adapter is usable on the current OS.