pgsql: Fix session-lifespan memory leak when a plperl function is

Log Message:
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Fix session-lifespan memory leak when a plperl function is redefined:
we have to tell Perl it can release its compiled copy of the function
text.  Noted by Alexey Klyukin.

Back-patch to 8.2 --- the problem exists further back, but this patch
won't work without modification, and it's probably not worth the trouble.

Tags:
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REL8_3_STABLE

Modified Files:
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    pgsql/src/pl/plperl:
        plperl.c (r1.136.2.4 -> r1.136.2.5)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/plperl.c?r1=1.136.2.4&r2=1.136.2.5)