Integrate:

Integrate:
[ 22034]
Fix bug #24383, where hashes with the :unique attribute weren't
getting made readonly on interpreter clone. Also, remove the
:unique attribute from the hashes in warnings.pm, since they may
later be modified by warnings::register.  Finally, adds tests for
the :unique attribute.
p4raw-link: @22034 on //depot/perl: 53c33732a73c90e26f613c11afdc5110e6a919ff

p4raw-id: //depot/maint-5.8/perl@22039
p4raw-integrated: from //depot/perl@22038 'copy in'
	ext/threads/t/problems.t (@21733..) 'merge in' lib/warnings.pm
	warnings.pl (@21167..) sv.c (@21971..)