Commit some half-done worldblock trie improvements

When you
* uncomment blocks_.erase(wb->global_position_);
* delete the 'return' at the beginning of worldblock::~worldblock()
* change only_put_non_interiory_blocks_in_the_trie = true; to false
    in the_decomposition_of_the_world_into_blocks.cpp

run and watch the segfaults.