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/scmutil.py

@@ -1066,7 +1066,7 b' def cleanupnodes('
         return
 
     # translate mapping's other forms
-    if not util.safehasattr(replacements, b'items'):
+    if not util.safehasattr(replacements, 'items'):
         replacements = {(n,): () for n in replacements}
     else:
         # upgrading non tuple "source" to tuple ones for BC