Changed defaults for ArrayByteBufferPool.

There are cases, for example in WebSocket, where we want to allocate
small buffers to write frame headers and then do a gathered write.
ArrayByteBufferPool had a minimum size of 64 bytes,
which was too big and always led to allocation rather than pooling,
leading to performance slowdowns.

Defaults are now minSize=0, increment=1024.

jetty-io/src/main/java/org/eclipse/jetty/io/ArrayByteBufferPool.java

@@ -33,7 +33,7 @@ public class ArrayByteBufferPool implements ByteBufferPool
 
     public ArrayByteBufferPool()
     {
-        this(64,2048,64*1024);
+        this(0,1024,64*1024);
     }
 
     public ArrayByteBufferPool(int minSize, int increment, int maxSize)