Increase PackOutputStream copy buffer to 64 KiB

Colby just pointed out to me the buffer was 16 KiB. This may
be very small for common objects. Increase to 64 KiB.

Change-Id: Ideecc4720655a57673252f7adb8eebdf2fda230d

org.eclipse.jgit/src/org/eclipse/jgit/internal/storage/pack/PackOutputStream.java

@@ -73,7 +73,7 @@ public final class PackOutputStream extends OutputStream {
 
 	private final byte[] headerBuffer = new byte[32];
 
-	private final byte[] copyBuffer = new byte[16 << 10];
+	private final byte[] copyBuffer = new byte[64 << 10];
 
 	private long checkCancelAt;