Here's another version of 0002 after cleaning up almost everything from David's review. I also added tests for ALTER STATISTICS in sql/alter_generic.sql which made me realize there were three crasher bug in here; fixed all those. It also made me realize that psql's \d was a little bit too generous with dropped columns in a stats object. That should all behave better now.
Thanks for fixing.
As you mentioned to me off-list about missing pg_dump support, I've gone and implemented that in the attached patch.
I followed how pg_dump works for indexes, and created pg_get_statisticsextdef() in ruleutils.c. I was unsure if I should be naming this pg_get_statisticsdef() instead.
I also noticed there's no COMMENT ON support either, so I added that too.