WIP: debugging scan support in masstree
WIP: deal with lcdf::Str()'s non-deep copy ctor

we now use std::string in test cases to hold key results.
this gets us farther in passing more test cases.
Merge remote-tracking branch 'github/master' into mbscan

Conflicts:
	btree.cc
	masstree_btree.h
mbtree: add a few test cases for reverse scans
txn_btree: equip with rsearch helpers
txn_btree: remove commented out txn_proto1 test cases
txn_btree: add some rsearch test case
Merge remote-tracking branch 'github/master' into mbscan
txn_btree: add another test case for rsearch
mbtree: respect callback's wishes to terminate scan
benchmarks: do order_status the right way

leave a flag to enable the hack for old silotree (the right way is
enabled by default)

this patch also fixes some un-necessary string ctor invocations
(implicit conversion of lcdf::Str -> std::string)