pgsql: Make ALTER .. SET SCHEMA do nothing, instead of throwing an ERRO

Make ALTER .. SET SCHEMA do nothing, instead of throwing an ERROR.

This was already true for CREATE EXTENSION, but historically has not
been true for other object types.  Therefore, this is a backward
incompatibility.  Per discussion on pgsql-hackers, everyone seems to
agree that the new behavior is better.

Marti Raudsepp, reviewed by Haribabu Kommi and myself

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/bc4996e61b98d41eacf991c18508b7a2305a68c6

Modified Files
--------------
src/backend/catalog/namespace.c             |   19 +++---------
src/backend/catalog/pg_constraint.c         |    3 +-
src/backend/commands/alter.c                |   12 +++++++-
src/backend/commands/tablecmds.c            |   14 ++++++---
src/backend/commands/typecmds.c             |   42 ++++++++++++++++-----------
src/include/catalog/namespace.h             |    3 +-
src/test/regress/expected/alter_generic.out |    1 +
src/test/regress/expected/alter_table.out   |    5 ++--
src/test/regress/sql/alter_generic.sql      |    1 +
src/test/regress/sql/alter_table.sql        |    4 ++-
10 files changed, 61 insertions(+), 43 deletions(-)