pgsql: Improve behavior of concurrent ALTER TABLE, and do some refactor

Improve behavior of concurrent ALTER TABLE, and do some refactoring.

ALTER TABLE (and ALTER VIEW, ALTER SEQUENCE, etc.) now use a
RangeVarGetRelid callback to check permissions before acquiring a table
lock.  We also now use the same callback for all forms of ALTER TABLE,
rather than having separate, almost-identical callbacks for ALTER TABLE
.. SET SCHEMA and ALTER TABLE .. RENAME, and no callback at all for
everything else.

I went ahead and changed the code so that no form of ALTER TABLE works
on foreign tables; you must use ALTER FOREIGN TABLE instead.  In 9.1,
it was possible to use ALTER TABLE .. SET SCHEMA or ALTER TABLE ..
RENAME on a foreign table, but not any other form of ALTER TABLE, which
did not seem terribly useful or consistent.

Patch by me; review by Noah Misch.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/1489e2f26a4c0318938b3085f50976512f321d84

Modified Files
--------------
src/backend/commands/alter.c     |    3 +-
src/backend/commands/tablecmds.c |  397 +++++++++++++++-----------------------
src/backend/tcop/utility.c       |   17 ++-
src/include/commands/tablecmds.h |    7 +-
4 files changed, 170 insertions(+), 254 deletions(-)