update_caps() can now do presence broadcasting.

As part of adding this feature:

    - fixed bug in update_caps() not assigning verstrings
    - fixed xep_0004 typo
    - can now use None as a roster key which will map to boundjid.bare
    - fixed using JID objects in disco node handlers
    - fixed failing test related to get_roster

Several of these bugs I've fixed before, so I either didn't push them
earlier, or I clobbered something when merging. *shrug*

sleekxmpp/roster/single.py

@@ -286,5 +286,16 @@ class RosterNode(object):
                 self.xmpp.event('sent_presence')
                 self.xmpp.sentpresence = True
 
+    def send_last_presence(self):
+        if self.last_status is None:
+            self.send_presence()
+        else:
+            pres = self.last_status
+            if self.xmpp.is_component:
+                pres['from'] = self.jid
+            else:
+                del pres['from']
+            pres.send()
+
     def __repr__(self):
         return repr(self._jids)