Why does AS_UNSET export the variable?

[Stepan Kasal]

Hello,
  I noticed that AS_UNSET uses export at the end.  So we have

        $as_unset ac_configure_args0 ||
          test "${ac_configure_args0+set}" != set ||
          { ac_configure_args0=; export ac_configure_args0; }

I do not think the export makes sense.  When unset is not available
and the variable is set, it is enough to set the neutralizing value.

If the variable was not exported, then child processes will not get
it, which is as good as if it was unset.  If the variable was
exported, the export is redundant.

What about the following patch?

Have a nice day,
        Stepan

autoconf-20080822-as-unset.patch
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