registry: Default to sorting sets of values

Not sorting them causes the config file to change when the bot writes
it, because order is nondeterministic.

This is usually fine, but can be annoying when configs are deployed
with Ansible.

Closes GH-1516

src/registry.py

@@ -875,6 +875,7 @@ class SpaceSeparatedListOfStrings(SpaceSeparatedListOf):
 class SpaceSeparatedSetOfStrings(SpaceSeparatedListOfStrings):
     __slots__ = ()
     List = set
+    sorted = True
 
 class CommaSeparatedListOfStrings(SeparatedListOf):
     __slots__ = ()
@@ -887,6 +888,7 @@ class CommaSeparatedSetOfStrings(SeparatedListOf):
     __slots__ = ()
     List = set
     Value = String
+    sorted = True
     def splitter(self, s):
         return re.split(r'\s*,\s*', s)
     joiner = ', '.join