The treap root pointer is now a CAS'ed atomic/unsafe.Pointer.
The treap root pointer is now a CAS'ed atomic/unsafe.Pointer.

With this change, concurrent reader goroutines should be able to work
with a single mutation goroutine, as long as the application's
StoreFile is concurrent "safe" (which vanilla os.File is not).

luci/gkvlite,steveyen/gkvlite