Introduce rcu::dealloc_rcu.

Which calls dealloc() after RCU is over. Requires some data
structure updates, b/c we need to store the size of the region
to be deallocated.
Add a Masstree btree variant. make M=1 to get it.
Masstree calls into the Silo RCU subsystem.
Actually compile
Insert_info includes both old & new version
Add masstree_btree print().
Return value on search; fix upper_compar_.
Btree print
Never run TestConcurrentBtree
Derp
New scan interface