pgsql: Fix incorrect documentation of plperl's method for accessing the

Log Message:
-----------
Fix incorrect documentation of plperl's method for accessing the number
of rows processed by a SPI query (David Fetter); also some other minor
editorial cleanup (Tom Lane).

Modified Files:
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pgsql/doc/src/sgml:
plperl.sgml (r2.30 -> r2.31)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/plperl.sgml.diff?r1=2.30&r2=2.31)