Summary
-------

Add cancel-on-interrupt ForkJoinTask adaptor

Problem
-------

Some potential FJ usages require that tasks are cancelled when their threads are interrupted, which is not the default policy for adapting Callables.

Solution
--------

Introduce a method adaptInterruptible that supports this policy.
An overview of the solution. Alternative solutions may be discussed;


Specification
-------------
    /**
     * Returns a new {@code ForkJoinTask} that performs the {@code call}
     * method of the given {@code Callable} as its action, and returns
     * its result upon {@link #join}, translating any checked exceptions
     * encountered into {@code RuntimeException}.  Additionally,
     * invocations of {@code cancel} with {@code mayInterruptIfRunning
     * true} will attempt to interrupt the thread performing the task.
     *
     * @param callable the callable action
     * @param <T> the type of the callable's result
     * @return the task
     *
     * @since 15
     */
    public static <T> ForkJoinTask<T> adaptInterruptible(Callable<? extends T> callable)