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

@@ -708,7 +708,7 b' class cmdalias:'
         }
         if name not in adefaults:
             raise AttributeError(name)
-        if self.badalias or util.safehasattr(self, b'shell'):
+        if self.badalias or util.safehasattr(self, 'shell'):
             return adefaults[name]
         return getattr(self.fn, name)