pgsql: Make ALTER TABLE revalidate uniqueness and exclusion constraints

Make ALTER TABLE revalidate uniqueness and exclusion constraints.

Failure to do so can lead to constraint violations.  This was broken by
commit 1ddc2703a936d03953657f43345460b9242bbed1 on 2010-02-07, so
back-patch to 9.0.

Noah Misch.  Regression test by me.

Branch
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master

Details
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http://git.postgresql.org/gitweb?p=postgresql.git;a=commitdiff;h=8ceb24568054232696dddc1166a8563bc78c900a

Modified Files
--------------
src/backend/catalog/index.c               |   43 ++++++++++++++++-------------
src/backend/commands/cluster.c            |    9 +++++-
src/backend/commands/indexcmds.c          |    4 +-
src/backend/commands/tablecmds.c          |    7 +++--
src/include/catalog/index.h               |    5 +++-
src/include/commands/cluster.h            |    1 +
src/test/regress/expected/alter_table.out |    4 +++
src/test/regress/sql/alter_table.sql      |    2 +
8 files changed, 48 insertions(+), 27 deletions(-)