Warnings "unrecognized node type" for some DDLs with log_statement = 'ddl'

Hi all,

While reviewing another patch, I have bumped into a couple of failures
when running installcheck if log_statement = 'ddl'. This pops
regression failures for 4 tests: object_address, alter_generic,
alter_operator and stats_ext involving commands CREATE STATISTICS and
ALTER OPERATOR.

You can as well reproduce the failures using simply that:
=# create table aa (a int, b int);
CREATE TABLE
=# CREATE STATISTICS aa_stat ON a, b FROM aa;
WARNING: 01000: unrecognized node type: 332
LOCATION: GetCommandLogLevel, utility.c:3357
ERROR: 42P17: extended statistics require at least 2 columns
LOCATION: CreateStatistics, statscmds.c:220
=# ALTER OPERATOR = (boolean, boolean) SET (RESTRICT = NONE);
WARNING: 01000: unrecognized node type: 294
LOCATION: GetCommandLogLevel, utility.c:3357
ALTER OPERATOR

Attached is a patch to fix all the failures I have spotted. As CREATE
STATISTICS is new in PG10, I am adding an open item as things come
from 7b504eb2. The problems of ALTER OPERATOR are introduced by 9.6.
Still I would suggest to fix everything at the same time. The problem
comes from GetCommandLogLevel() which forgot to add T_CreateStatsStmt
and T_AlterOperatorStmt. I have noticed as well that
T_AlterCollationStmt was missing.

Thanks,
--
Michael