Summary
-------

Update `Long.valueOf(long)` to require caching of values [-128, 127]. The implementation has always cached in this range and the corresponding `valueOf` methods in other integral wrapper classes have been required to cache in this range too.

Problem
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Other parts of the platform rely on `Long.valueOf(long)` to cache, but the method is not required to do that caching.

Solution
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Update the specification to require caching.

Specification
-------------

    diff -r f909f09569ca src/java.base/share/classes/java/lang/Long.java
    --- a/src/java.base/share/classes/java/lang/Long.java    Wed Apr 18 21:10:09 2018 -0700
    +++ b/src/java.base/share/classes/java/lang/Long.java    Tue Apr 24 17:25:24 2018 -0700
    @@ -1164,10 +1164,8 @@
          * significantly better space and time performance by caching
          * frequently requested values.
          *
    -     * Note that unlike the {@linkplain Integer#valueOf(int)
    -     * corresponding method} in the {@code Integer} class, this method
    -     * is <em>not</em> required to cache values within a particular
    -     * range.
    +     * This method will always cache values in the range -128 to 127,
    +     * inclusive, and may cache other values outside of this range.
          *
          * @param  l a long value.
          * @return a {@code Long} instance representing {@code l}.