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/templateutil.py

@@ -858,7 +858,7 b' def flatten(context, mapping, thing):'
         )
     elif thing is None:
         pass
-    elif not util.safehasattr(thing, b'__iter__'):
+    elif not util.safehasattr(thing, '__iter__'):
         yield pycompat.bytestr(thing)
     else:
         for i in thing: