syncbase/vsync: DAG improvements & more tests.

* Support conflict detection where the DAG fragments have no
  common ancestor (evolved from disjoint pasts).
* Switch sync tests to using leveldb instead of memstore.
* Guard the random number generator with a mutex.
* Add more DAG tests.

Change-Id: Ic46ce0109cde04d8b4eaa93ae001ee28b2a65d12
13 files changed
tree: 8edcd413072dd445d13a6e7ba485ce47ab008361
  1. services/