pycompat: when setting attrs, ensure we use sysstr

The custom module importer was making these bytes, so when we poked
values into self.__dict__ we had bytes instead of unicode on py3 and
it didn't work.

mercurial/pycompat.py

@@ -74,7 +74,9 b' class _pycompatstub(object):'
 
     def _registeraliases(self, origin, items):
         """Add items that will be populated at the first access"""
-        self._aliases.update((item.replace('_', '').lower(), (origin, item))
+        items = map(sysstr, items)
+        self._aliases.update(
+            (item.replace(sysstr('_'), sysstr('')).lower(), (origin, item))
                              for item in items)
 
     def __getattr__(self, name):