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/commandserver.py

@@ -559,7 +559,7 b' class unixforkingservice:'
         self.ui = ui
         self.repo = repo
         self.address = opts[b'address']
-        if not util.safehasattr(socket, b'AF_UNIX'):
+        if not util.safehasattr(socket, 'AF_UNIX'):
             raise error.Abort(_(b'unsupported platform'))
         if not self.address:
             raise error.Abort(_(b'no socket path specified with --address'))