pgsql: Fix propagating attnotnull in multiple inheritance

Fix propagating attnotnull in multiple inheritance

In one of the many strange corner cases of multiple inheritance being
used, commit b0e96f311985 missed a CommandCounterIncrement() call after
updating the attnotnull flag during ALTER TABLE ADD COLUMN, which caused
a catalog tuple to be update attempted twice in the same command, giving
rise to a "tuple already updated by self" error. Add the missing call
to solve that, and a test case that reproduces the scenario.

As a (perhaps surprising) secondary effect, this CCI addition triggers
another behavior change: when a primary key is added to a parent
partitioned table and the column in an existing partition does not have
a not-null constraint, we no longer error out. This will probably be a
welcome change by some users, and I think it's unlikely that anybody
will miss the old behavior.

Reported-by: Alexander Lakhin <exclusion(at)gmail(dot)com>
Discussion: http://postgr.es/m/045dec3f-9b3d-aa44-0c99-85f6992306c7@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c3709100be73ad5af7ff536476d4d713bca41b1a

Modified Files
--------------
src/backend/commands/tablecmds.c | 4 ++++
src/test/regress/expected/constraints.out | 10 +++++++++-
src/test/regress/expected/inherit.out | 8 ++++++++
src/test/regress/sql/constraints.sql | 7 +++++++
src/test/regress/sql/inherit.sql | 7 +++++++
5 files changed, 35 insertions(+), 1 deletion(-)