btree: node locks now return version #s of the locked node

also some naming cleanup
checkpoint: use FindRespLeaf() in insert
btree: checkpoint- insert optimization passes test cases
be more paranoid about cache alignment
tuple: remove unused code
btree: fix up ownership checking debugging tools
btree: remove no longer holds locks on trie leaf nodes

same optimization as insert- is actually necessary to avoid a potential
deadlock amongst concurrent inserts and removes
btree: slightly more optimized search
benchmarks: slightly tweak experiment configuration