pgsql: Don't trust deferred-unique indexes for join removal.

Don't trust deferred-unique indexes for join removal.

The uniqueness condition might fail to hold intra-transaction, and assuming
it does can give incorrect query results.  Per report from Marti Raudsepp,
though this is not his proposed patch.

Back-patch to 9.0, where both these features were introduced.  In the
released branches, add the new IndexOptInfo field to the end of the struct,
to try to minimize ABI breakage for third-party code that may be examining
that struct.

Branch
------
REL9_0_STABLE

Details
-------
http://git.postgresql.org/pg/commitdiff/9fbb3edff085f2f004c24b988b43c7cd4f132e2f

Modified Files
--------------
src/backend/nodes/outfuncs.c          |    1 +
src/backend/optimizer/path/indxpath.c |    7 ++++---
src/backend/optimizer/util/plancat.c  |    6 ++++++
src/backend/utils/adt/selfuncs.c      |    4 +++-
src/include/nodes/relation.h          |    2 ++
5 files changed, 16 insertions(+), 4 deletions(-)