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/LinkedHashMap.java

@@ -131,7 +131,7 @@ public class LinkedHashMap<K, V> extends HashMap<K, V> {
     }
 
     public <T> T[] toArray(T[] array) {
-      return Collections.toArray(this, array);
+      return avian.Data.toArray(this, array);
     }
 
     public void clear() {
@@ -169,7 +169,7 @@ public class LinkedHashMap<K, V> extends HashMap<K, V> {
     }
 
     public <T> T[] toArray(T[] array) {
-      return Collections.toArray(this, array);
+      return avian.Data.toArray(this, array);
     }
 
     public void clear() {
@@ -177,7 +177,7 @@ public class LinkedHashMap<K, V> extends HashMap<K, V> {
     }
 
     public Iterator<K> iterator() {
-      return new Collections.KeyIterator(new MyIterator());
+      return new avian.Data.KeyIterator(new MyIterator());
     }
   }
 
@@ -230,7 +230,7 @@ public class LinkedHashMap<K, V> extends HashMap<K, V> {
     }
 
     public <T> T[] toArray(T[] array) {
-      return Collections.toArray(this, array);
+      return avian.Data.toArray(this, array);
     }
 
     public void clear() {
@@ -238,7 +238,7 @@ public class LinkedHashMap<K, V> extends HashMap<K, V> {
     }
 
     public Iterator<V> iterator() {
-      return new Collections.ValueIterator(new MyIterator());
+      return new avian.Data.ValueIterator(new MyIterator());
     }
   }