added unbound to external deps

external/unbound/libunbound/python/doc/examples/example3.rst

@@ -0,0 +1,36 @@
+.. _example_asynch:
+
+==============================
+Asynchronous lookup
+==============================
+
+This example performs the name lookup in the background. 
+The main program keeps running while the name is resolved. 
+
+::
+
+	#!/usr/bin/python
+	import time
+	import unbound
+	
+	ctx = unbound.ub_ctx()
+	ctx.resolvconf("/etc/resolv.conf")
+	
+	def call_back(my_data,status,result):
+		print "Call_back:", my_data
+		if status == 0 and result.havedata:
+			print "Result:", result.data.address_list
+			my_data['done_flag'] = True
+	
+	
+	my_data = {'done_flag':False,'arbitrary':"object"}
+	status, async_id = ctx.resolve_async("www.seznam.cz", my_data, call_back, unbound.RR_TYPE_A, unbound.RR_CLASS_IN)
+	        
+	while (status == 0) and (not my_data['done_flag']):
+		status = ctx.process()
+		time.sleep(0.1)
+	
+	if (status != 0):
+		print "Resolve error:", unbound.ub_strerror(status)
+
+The :meth:`unbound.ub_ctx.resolve_async` method is able to pass on any Python object. In this example, we used a dictionary object `my_data`.