implement ConcurrentHashMap and AtomicReferenceArray

This is the simplest possible ConcurrentHashMap I could come up with
that works and is actually concurrent in the way one would expect.
It's pretty unconventional, being based on a persistent red-black
tree, and not particularly memory-efficient or cache-friendly.  I
think this is a good place to start, though, and it should perform
reasonably well for most workloads.  Patches for a more efficient
implementation are welcome!

I also implemented AtomicReferenceArray, since I was using it in my
first, naive attempt to implement ConcurrentHashMap.

I had to do a bit of refactoring, including moving some non-standard
stuff from java.util.Collections to avian.Data so I could make it
available to code outside the java.util package, which is why I had to
modify several unrelated files.

classpath/java/util/TreeMap.java

@@ -42,7 +42,7 @@ public class TreeMap<K,V> implements Map<K,V> {
   }
 
   public String toString() {
-    return Collections.toString(this);
+    return avian.Data.toString(this);
   }
 
   public V get(Object key) {
@@ -164,7 +164,7 @@ public class TreeMap<K,V> implements Map<K,V> {
     }
 
     public <T> T[] toArray(T[] array) {
-      return Collections.toArray(this, array);      
+      return avian.Data.toArray(this, array);      
     }
 
     public void clear() {
@@ -172,7 +172,7 @@ public class TreeMap<K,V> implements Map<K,V> {
     }
 
     public Iterator<K> iterator() {
-      return new Collections.KeyIterator(set.iterator());
+      return new avian.Data.KeyIterator(set.iterator());
     }
   }
 
@@ -225,7 +225,7 @@ public class TreeMap<K,V> implements Map<K,V> {
     }
 
     public <T> T[] toArray(T[] array) {
-      return Collections.toArray(this, array);      
+      return avian.Data.toArray(this, array);      
     }
 
     public void clear() {
@@ -233,7 +233,7 @@ public class TreeMap<K,V> implements Map<K,V> {
     }
 
     public Iterator<V> iterator() {
-      return new Collections.ValueIterator(set.iterator());
+      return new avian.Data.ValueIterator(set.iterator());
     }
   }