safehasattr: pass attribute name as string instead of bytes

This is a step toward replacing `util.safehasattr` usage with plain `hasattr`.
The builtin function behave poorly in Python2 but this was fixed in Python3.

These change are done one by one as they tend to have a small odd to trigger
puzzling breackage.

mercurial/cmdutil.py

@@ -1450,7 +1450,7 b' def openstorage(repo, cmd, file_, opts, '
         if returnrevlog:
             if isinstance(r, revlog.revlog):
                 pass
-            elif util.safehasattr(r, b'_revlog'):
+            elif util.safehasattr(r, '_revlog'):
                 r = r._revlog  # pytype: disable=attribute-error
             elif r is not None:
                 raise error.InputError(