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/dispatch.py

@@ -734,7 +734,7 b' class cmdalias:'
             self.name,
             self.definition,
         )
-        if util.safehasattr(self, b'shell'):
+        if util.safehasattr(self, 'shell'):
             return self.fn(ui, *args, **opts)
         else:
             try: