pgsql: Fix a few minor mistakes in header comments.

Log Message:
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Fix a few minor mistakes in header comments. From Qingqing Zhou.

Modified Files:
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pgsql/src/port:
getrusage.c (r1.8 -> r1.9)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/getrusage.c.diff?r1=1.8&r2=1.9)
gettimeofday.c (r1.5 -> r1.6)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/port/gettimeofday.c.diff?r1=1.5&r2=1.6)