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/chgserver.py

@@ -236,7 +236,7 b' def _newchgui(srcui, csystem, attachio):'
             # will behave differently (i.e. write to stdout).
             if (
                 out is not self.fout
-                or not util.safehasattr(self.fout, b'fileno')
+                or not util.safehasattr(self.fout, 'fileno')
                 or self.fout.fileno() != procutil.stdout.fileno()
                 or self._finoutredirected
             ):