playing with 1/2 sized chunks. small tests run, this case failed in
test.py and broke it out as separate test. I hardwired the chunk size
locally like this in ValueArray.java:
-  public static final int LOG_CHK = 20; // Chunks are 1<<20, or 1Meg
+  public static final int LOG_CHK = 10; // Chunks are 1<<20, or 1Meg
   public static final long CHUNK_SZ = 1L << LOG_CHK;

failure seems simple, complains about dataset format. normally runs
fine.