RFR 8015798: Rename IntStream.longs/doubles and LongStream.doubles to asXxxStream

[Paul Sandoz]

Hi,

The following patch renames the methods 
IntStream.longs/doubles/LongStream.doubles, as decided by the JSR-335 EG which 
agreed the new names better convey transformation to another type of primitive 
stream:

  http://cr.openjdk.java.net/~psandoz/tl/JDK-8015798-asXxxStream/webrev/
 
  IntStream.longs -> asLongStream
  IntStream.doubles -> asDoubleStream
  LongStream.doubles -> asDoubleStream

Paul.