pgsql: Add plperl.on_perl_init setting to provide for initializing the

Log Message:
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Add plperl.on_perl_init setting to provide for initializing the perl library on load. Also, handle END blocks in
plperl.
Database access is disallowed during both these operations, although it might be allowed in END blocks in future.

Patch from Tim Bunce.

Modified Files:
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    pgsql/doc/src/sgml:
        plperl.sgml (r2.76 -> r2.77)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/plperl.sgml?r1=2.76&r2=2.77)
    pgsql/src/pl/plperl:
        plc_perlboot.pl (r1.3 -> r1.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/plc_perlboot.pl?r1=1.3&r2=1.4)
        plperl.c (r1.162 -> r1.163)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/plperl.c?r1=1.162&r2=1.163)
    pgsql/src/pl/plperl/sql:
        plperl_plperlu.sql (r1.2 -> r1.3)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/sql/plperl_plperlu.sql?r1=1.2&r2=1.3)

Added Files:
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    pgsql/src/pl/plperl/sql:
        plperl_end.sql (r1.1)

(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/pl/plperl/sql/plperl_end.sql?rev=1.1&content-type=text/x-cvsweb-markup)