Remove overly-pessimistic statement about constraint exclusion.

As of 9.2, constraint exclusion should work okay with prepared statements:
the planner will try custom plans with actual values of the parameters,
and observe that they are a lot cheaper than the generic plan, and thus
never fall back to using the generic plan.  Noted by Tatsuhito Kasahara.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/6e2e12c9477c3b48854433251ebca9709be3e87b

Modified Files
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doc/src/sgml/ddl.sgml |   10 +++++-----
1 files changed, 5 insertions(+), 5 deletions(-)

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