pgsql: Improve release notes' description of Teodor's fixes for polygon

Log Message:
-----------
Improve release notes' description of Teodor's fixes for polygon overlaps
and contains operators.

Modified Files:
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pgsql/doc/src/sgml:
release-9.0.sgml (r2.54 -> r2.55)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release-9.0.sgml?r1=2.54&r2=2.55)