pgsql: Allow ALTER TYPE .. ADD ATTRIBUTE .. CASCADE to recurse to desce

Allow ALTER TYPE .. ADD ATTRIBUTE .. CASCADE to recurse to descendants.

Without this, adding an attribute to a typed table with an inheritance
child fails, which is surprising.

Noah Misch, with minor changes by me.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/a0e8df527ec24e8dba98f295c0e2ab6ccf3e5d2c

Modified Files
--------------
doc/src/sgml/ref/alter_type.sgml          |    2 +-
src/backend/commands/tablecmds.c          |    5 +++--
src/test/regress/expected/alter_table.out |   15 +++++++++++++++
src/test/regress/sql/alter_table.sql      |    4 ++++
4 files changed, 23 insertions(+), 3 deletions(-)