It is not enough to go over all column types and register the UDTs. UDTs
might be nested in other types, like collections. One has to do a
traversal of the type tree and register every UDT on the way. That is
what this patch does.
This function is used by the query and write operations, which should
now both work with nested UDTs.
Add a test which fails before and passes after this patch.
8dbcd8a0b3