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

@@ -868,7 +868,7 b' def flatten(context, mapping, thing):'
                 yield i
             elif i is None:
                 pass
-            elif not util.safehasattr(i, b'__iter__'):
+            elif not util.safehasattr(i, '__iter__'):
                 yield pycompat.bytestr(i)
             else:
                 for j in flatten(context, mapping, i):