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/templatefilters.py

@@ -346,7 +346,7 b' def json(obj, paranoid=True):'
             for k, v in sorted(obj.items())
         ]
         return b'{' + b', '.join(out) + b'}'
-    elif util.safehasattr(obj, b'__iter__'):
+    elif util.safehasattr(obj, '__iter__'):
         out = [json(i, paranoid) for i in obj]
         return b'[' + b', '.join(out) + b']'
     raise error.ProgrammingError(b'cannot encode %r' % obj)