RFR 8071477: Better Spliterator implementations for String.chars() and String.codePoints()

[Paul Sandoz]

Hi,

http://cr.openjdk.java.net/~psandoz/jdk9/JDK-8071477-String-spliterators/webrev/

This patch implements better spliterators for 
String/Buffer/Builder.chars/codePoints than those provided by the default 
methods on CharSequence.

The test java/lang/CharSequence/DefaultTest.java is removed as i now pass the 
spliterators through the grinder of the spliterator-and-traversing tests.

Thanks,
Paul.