Corrected test errors.

There was a bug in the XML compare method.

sleekxmpp/stanza/presence.py

@@ -78,7 +78,9 @@ class Presence(RootStanza):
         Arguments:
             show -- Must be one of: away, chat, dnd, or xa.
         """
-        if show in self.showtypes:
+        if show is None:
+            self._delSub('show')
+        elif show in self.showtypes:
             self._setSubText('show', text=show)
         return self
 
@@ -99,6 +101,14 @@ class Presence(RootStanza):
             self['show'] = value
         return self
 
+    def delType(self):
+        """
+        Remove both the type attribute and the <show> element.
+        """
+        self._delAttr('type')
+        self._delSub('show')
+
+
     def setPriority(self, value):
         """
         Set the entity's priority value. Some server use priority to

sleekxmpp/xmlstream/stanzabase.py

@@ -423,7 +423,9 @@ class ElementBase(object):
                     self._delAttr(attrib)
         elif attrib in self.plugin_attrib_map:
             if attrib in self.plugins:
+                xml = self.plugins[attrib].xml
                 del self.plugins[attrib]
+                self.xml.remove(xml)
         return self
 
     def _setAttr(self, name, value):
@@ -511,7 +513,7 @@ class ElementBase(object):
         element = self.xml.find(name)
 
         if not text and not keep:
-            return self.__delitem__(name)
+            return self._delSub(name)
 
         if element is None:
             # We need to add the element. If the provided name was