Like the begin-concurrent-wal2 branch, this branch contains both the and
CONCURRENT]" enhancements. It also has:

   *  the mutex-free PRNG,
   *  the mutex-free shmlock enhancement for VFS unix-excl,
   *  the "PRAGMA noop_update" feature (hence the "pnu" in the branch name), and
   *  the sqlite3_wal_info() API.