Add an "online" contact sorting method

- put the online contacts at the beginning of the list
- allows, e.g. jid_reverse_online_reverse, to put offline contacts at
  the start of the group, in alphabetical order

data/default_config.cfg

@@ -231,6 +231,7 @@ roster_show_offline = false
 #   - show: sort by show (available/away/xa/…)
 #   - name: sort by roster name (if no name, then the bare jid is used)
 #   - resource: sort by resource number
+#   - online: sort by online presence (online or not)
 # You can arrange them however you like, and you have to separate them with
 # underscores "_". Keep in mind that if there are more than 3 or 4 your sorting
 # is most likely inefficient.

doc/en/configure.txt

@@ -289,8 +289,9 @@ section of this documentation.
     * reverse: reverse the current sorting
     * jid: sort by JID (alphabetical order)
     * show: sort by show (available/away/xa/…)
-    * name: Sort by roster name (if no name, then the bare jid is used)
-    * resource: Sort by resource number
+    * name: sort by roster name (if no name, then the bare jid is used)
+    * resource: sort by resource number
+    * online: sort by online presence (online or not)
 
   Those methods can be arranged however you like, and they have to be
   separated by underscores ("_"). If there are more than 3 or 4 chained

src/roster.py

@@ -255,11 +255,16 @@ def sort_resource_nb(contact):
 def sort_name(contact):
     return contact.name.lower() or contact.bare_jid
 
+def sort_online(contact):
+    result = sort_show(contact)
+    return 0 if result < 5 else 1
+
 SORTING_METHODS = {
     'jid': sort_jid,
     'show': sort_show,
     'resource': sort_resource_nb,
     'name': sort_name,
+    'online': sort_online,
 }
 
 class RosterGroup(object):