ui.py: make walkconfig use configitems

Also make it sort the available config sections while we're at it.

mercurial/ui.py

@@ -142,15 +142,13 b' class ui(object):'
         for (section, name), value in self.overlay.iteritems():
             yield section, name, value
             seen[section, name] = 1
-        for section in self.cdata.sections():
-            try:
-                for name, value in self.cdata.items(section):
+        sections = self.cdata.sections()
+        sections.sort()
+        for section in sections:
+            for name, value in self.configitems(section):
                     if (section, name) in seen: continue
                     yield section, name, value.replace('\n', '\\n')
                     seen[section, name] = 1
-            except ConfigParser.InterpolationError, inst:
-                raise util.Abort(_("Error in configuration section [%s]:\n%s")
-                                 % (section, inst))
         if self.parentui is not None:
             for parent in self.parentui.walkconfig(seen):
                 yield parent