Serialize descriptor with each brtnode (leaf and nonleaf) 
Deserialize descriptor with each brtnode (to be thrown away). 
    Don't malloc+memdup the descriptor for brtnodes, since that would waste time.




git-svn-id: file:///svn/toku/tokudb@11200 c7de825b-a66e-492c-adef-691d508d4ae1