test Cases for pred/succ
 * Empty tree
  * Pred return nothing.
  * Succ return nothing.
 * 1 element tree.
  * Pred
  * Before
  * left
  * middle
  * right
  * after.
 * Succ
  * Before
  * left
  * middle
  * right
  * after
 * 2 element tree.
  * Pred, Succ
   * In empty space
    * Nothing to the left/Right (pred/succ) respectively.
    * something to the left/right (pred/succ) respectively.
   * On left endpoint.
    * Nothing to the left/Right (pred/succ) respectively.
    * something to the left/right (pred/succ) respectively.
   * On right endpoint.
    * Nothing to the left/Right (pred/succ) respectively.
    * something to the left/right (pred/succ) respectively.
   * In middle of range.
    * Nothing to the left/Right (pred/succ) respectively.
    * something to the left/right (pred/succ) respectively.


git-svn-id: file:///svn/tokudb@1774 c7de825b-a66e-492c-adef-691d508d4ae1