I added some extra tests for different cases of use of automatic partition creation.
v3-0002 can be applied on top of the original v2 patch for correct work with some corner cases with constraints included in this test.
As for immediate/deferred I think that now only available now is immediate, so using word IMMEDIATE seems a little bit redundant to me. We may introduce this word together with adding DEFERRED option. However, my opinion is not in strong opposition to both options. Оther opinions are very much welcome!
