Revert "Primary Key Guessing Implemented"

This reverts commit 13c67c478fcaf87b1bde1b634154063c2acf2abc.

Conflicts:

	core/MY_Model.php
Revert "Test Case Implement"

This reverts commit 931d719f6f753c3d98935fe8ffe73636d0acd6f8.

Conflicts:

	core/MY_Model.php
Merge with the upstream project.