py3: avoid use of basestring

"In this case, result is a source variable of a list to be returned, it
shouldn't be unicode. Hence we can use bytes instead of basestring here." -Yuya

mercurial/ui.py

@@ -535,7 +535,7 b' class ui(object):'
         result = self.config(section, name, untrusted=untrusted)
         if result is None:
             result = default or []
-        if isinstance(result, basestring):
+        if isinstance(result, bytes):
             result = _configlist(result.lstrip(' ,\n'))
             if result is None:
                 result = default or []

tests/test-check-py3-commands.t

@@ -9,6 +9,6 b' The full traceback is hidden to have a s'
   >   $PYTHON3 `which hg` $cmd 2>&1 2>&1 | tail -1
   > done
   version
-  NameError: name 'basestring' is not defined
+  TypeError: Can't convert 'bytes' object to str implicitly
   debuginstall
-  NameError: name 'basestring' is not defined
+  TypeError: Can't convert 'bytes' object to str implicitly