Only uses lock tree if both txns and locking system are enabled.
If TXN only is enabled, it implies only one txn at a time: no lock tree needed.
If LOCK only is enabled, it implies no txns, therefore only ephemeral locks needed (lock tree not needed)
If neither are enabled, clearly lock tree is not needed.

git-svn-id: file:///svn/tokudb@2193 c7de825b-a66e-492c-adef-691d508d4ae1