Store 2050 blocks in the BoundedOverheadBlockStore memory cache. This eliminates the delay on difficulty transitions. We now regularly hit 500 blocks per second, ie, we are sender-constrained.

src/com/google/bitcoin/store/BoundedOverheadBlockStore.java

@@ -52,7 +52,7 @@ public class BoundedOverheadBlockStore implements BlockStore {
     private LinkedHashMap<Sha256Hash, StoredBlock> blockCache = new LinkedHashMap<Sha256Hash, StoredBlock>() {
         @Override
         protected boolean removeEldestEntry(Map.Entry<Sha256Hash, StoredBlock> entry) {
-            return size() > 100;  // This was chosen arbitrarily.
+            return size() > 2050;  // Slightly more than the difficulty transition period.
         }
     };
     // Use a separate cache to track get() misses. This is to efficiently handle the case of an unconnected block