fixed before_delete and after_delete docs
failing test for setting NULL and then saving
fix for not nullifying hasone association on save; introduces regression in test_collect_children
using Testcase_Database in HasOneTest for database transactions
Merge pull request #12 from hkdobrev/fix-null-save

Setting NULL to hasone and saving does not work
fixed usage of array_key_exists in Jam_Array when used from Jam_Array_Model
Merge pull request #7 from vkuzmov/patch-1

fixed before_delete and after_delete docs
`before_validate` and `after_validate` are `before_check` and `after_check`

The events which are triggered on `check()` are not `before_validate` and `after_validate`, but `before_check` and `after_check`.

https://github.com/OpenBuildings/jam/blob/6b59ffcbc4e23869a9cca52d2520768407203526/classes/Kohana/Jam/Validated.php#L329