pgsql: Update "Conflicting lock modes" to show as conflict, add

Log Message:
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Update "Conflicting lock modes" to show as conflict, add
current/requested headings, add link to table from text.

Modified Files:
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pgsql/doc/src/sgml:
mvcc.sgml (r2.68 -> r2.69)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/mvcc.sgml.diff?r1=2.68&r2=2.69)