pgsql: Improve a couple of 9.2 release note entries.

Improve a couple of 9.2 release note entries.

Clarify the compatibility notes about EXTRACT() and about statistics
timing columns.

Branch
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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/a63b7744fa4abdabc977dd4525d0444ddf10f9ed

Modified Files
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doc/src/sgml/release-9.2.sgml | 37 ++++++++++++++++++++++---------------
1 files changed, 22 insertions(+), 15 deletions(-)