Tweak PeerGroup thread priority. Resolves issue 67.

src/com/google/bitcoin/core/PeerGroup.java

@@ -402,7 +402,7 @@ public class PeerGroup {
             // Lower the priority of the peer threads. This is to avoid competing with UI threads created by the API
             // user when doing lots of work, like downloading the block chain. We select a priority level one lower
             // than the parent thread, or the minimum.
-            t.setPriority(Math.max(Thread.MIN_PRIORITY, group.getMaxPriority() - 1));
+            t.setPriority(Math.max(Thread.MIN_PRIORITY, Thread.currentThread().getPriority() - 1));
             t.setDaemon(true);
             return t;
         }