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/crecord.py

@@ -1944,7 +1944,7 b' are you sure you want to review/edit and'
         """
 
         origsigwinch = sentinel = object()
-        if util.safehasattr(signal, b'SIGWINCH'):
+        if util.safehasattr(signal, 'SIGWINCH'):
             origsigwinch = signal.signal(signal.SIGWINCH, self.sigwinchhandler)
         try:
             return self._main(stdscr)