pgsql: Add an "incompatibility" entry to 9.1 release notes about CREATE

Add an "incompatibility" entry to 9.1 release notes about CREATE EXTENSION.

We've now seen more than one gripe from somebody who didn't get the memo
about how to install contrib modules in 9.1. Try to make it a little more
prominent that you aren't supposed to call the scripts directly anymore.

Branch
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REL9_1_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/a3850a5f7582ebe328d2506873e31aac2b01d51b

Modified Files
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doc/src/sgml/release-9.1.sgml | 18 ++++++++++++++++++
1 files changed, 18 insertions(+), 0 deletions(-)