The ALTER TABLE ALTER TYPE implementation can issue DROP INDEX and
CREATE INDEX to refit existing indexes for the new column type.  Since
this CREATE INDEX is an implementation detail of an index alteration,
the ensuing DefineIndex() should skip ACL checks specific to index
creation.  It already skips the namespace ACL check.  Make it skip the
tablespace ACL check, too.  Back-patch to 9.2 (all supported versions).

Reviewed by Tom Lane.