Ensure plperl strings are always correctly UTF8 encoded.

Amit Khandekar and Alex Hunsaker.

Backpatched to 9.1 where the problem first occurred.

src/pl/plperl/sql/plperl.sql

@@ -423,6 +423,15 @@ DO $do$ use strict; my $name = "foo"; my $ref = $$name; $do$ LANGUAGE plperl;
 -- yields "ERROR:  Useless use of sort in scalar context."
 DO $do$ use warnings FATAL => qw(void) ; my @y; my $x = sort @y; 1; $do$ LANGUAGE plperl;
 
+--
+-- Make sure strings are validated
+-- Should fail for all encodings, as nul bytes are never permitted.
+--
+CREATE OR REPLACE FUNCTION perl_zerob() RETURNS TEXT AS $$
+  return "abcd\0efg";
+$$ LANGUAGE plperlu;
+SELECT perl_zerob();
+
 -- make sure functions marked as VOID without an explicit return work
 CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
    $_SHARED{myquote} = sub {