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

@@ -234,7 +234,7 b' def callcatch(ui, func):'
         ui.error(_(b"abort: error: %s\n") % stringutil.forcebytestr(reason))
     except (IOError, OSError) as inst:
         if (
-            util.safehasattr(inst, b"args")
+            util.safehasattr(inst, "args")
             and inst.args
             and inst.args[0] == errno.EPIPE
         ):