added separate tostring files

tests/test_presencestanzas.py

@@ -0,0 +1,15 @@
+import unittest
+
+class testpresencestanzas(unittest.TestCase):
+
+	def setUp(self):
+		import sleekxmpp.stanza.presence as p
+		self.p = p
+	
+	def testPresenceShowRegression(self):
+		"Regression check presence['type'] = 'dnd' show value working"
+		p = self.p.Presence()
+		p['type'] = 'dnd'
+		self.failUnless(str(p) == "<presence><show>dnd</show></presence>")
+
+suite = unittest.TestLoader().loadTestsFromTestCase(testpresencestanzas)