8016251: Balanced spliterator for SpinedBuffer

[Paul Sandoz]

Hi,

This patch contains the following changes:

1) implements balanced splits for the spliterator of SpinedBuffer, which is contributed by Peter Levart; and

2) syncs lambda's version SpinedBuffer with tl, hence why there are some other changes they may not be entirely obvious until other code follows later on but will make that process easier e.g. the renaming of asXxxArray to asPrimitiveArray or the method SpinedBuffer.OfPrimitive.newArray changing from protected to public.

  http://cr.openjdk.java.net/~psandoz/tl/JDK-8016251-spinedBuffer-splitr/webrev/

Paul.