pgsql: Fix mistakes in SGML markup.

Log Message:
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Fix mistakes in SGML markup. From David Fetter.

Modified Files:
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pgsql/doc/src/sgml:
charset.sgml (r2.67 -> r2.68)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/charset.sgml.diff?r1=2.67&r2=2.68)
planstats.sgml (r1.2 -> r1.3)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/planstats.sgml.diff?r1=1.2&r2=1.3)
runtime.sgml (r1.308 -> r1.309)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/runtime.sgml.diff?r1=1.308&r2=1.309)