djangoplugins uniq constraint: use id instead of index

was getting error messages about duplicate keys, looks like the id
counter is automatically incremented as a uniq field but that index
field might not be as a plain integer field (not handled by postgres at
all?)

djangoplugins/management/commands/syncplugins.py

@@ -107,10 +107,10 @@ def plugins(self, point, point_inst):
         src = self.get_classes_dict(point.plugins)
         dst = self.get_instances_dict(point_inst.plugin_set.all())
 
-        for _i, (plugin, inst) in enumerate(self.available(src, dst, Plugin)):
+        for plugin, inst in self.available(src, dst, Plugin):
             inst.point = point_inst
             inst.name = getattr(plugin, 'name', None)
-            inst.index = _i
+            inst.id = getattr(plugin, 'id')
             if hasattr(plugin, 'title'):
                 inst.title = six.text_type(getattr(plugin, 'title'))
             inst.save()

djangoplugins/migrations/0002_add_id_to_plugins_uniq.py

@@ -14,6 +14,6 @@ class Migration(migrations.Migration):
     operations = [
         migrations.AlterUniqueTogether(
             name='plugin',
-            unique_together=set([('point', 'name', 'index')]),
+            unique_together=set([('point', 'name', 'id')]),
         ),
     ]