pgsql: Make an editorial pass over the 9.0 release notes.

Log Message:
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Make an editorial pass over the 9.0 release notes.

This is mostly about grammar, style, and presentation, though I did find
a few small factual errors.

Tags:
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REL9_0_STABLE

Modified Files:
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pgsql/doc/src/sgml:
config.sgml (r1.294.2.6 -> r1.294.2.7)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/config.sgml?r1=1.294.2.6&r2=1.294.2.7)
ddl.sgml (r1.93.2.1 -> r1.93.2.2)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ddl.sgml?r1=1.93.2.1&r2=1.93.2.2)
release-9.0.sgml (r2.39.2.6 -> r2.39.2.7)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release-9.0.sgml?r1=2.39.2.6&r2=2.39.2.7)