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/wireprotov1peer.py

@@ -483,7 +483,7 b' class wirepeer(repository.peer):'
         else:
             heads = wireprototypes.encodelist(heads)
 
-        if util.safehasattr(bundle, b'deltaheader'):
+        if util.safehasattr(bundle, 'deltaheader'):
             # this a bundle10, do the old style call sequence
             ret, output = self._callpush(b"unbundle", bundle, heads=heads)
             if ret == b"":