pgsql: Fix a few typos in comments.

Log Message:
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Fix a few typos in comments.

Modified Files:
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pgsql/src/pl/plpgsql/src:
pl_comp.c (r1.82 -> r1.83)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_comp.c.diff?r1=1.82&r2=1.83)
pl_exec.c (r1.122 -> r1.123)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpgsql/src/pl_exec.c.diff?r1=1.122&r2=1.123)