RFR (trivial) 8029141: Add @FunctionalInterface annotation to Callable interface

[Chris Hegarty]

A trivial one on our JDK8 list. Doug has already accepted this into the 
166 CVS.

Stuart brought this up a while back, and given our short deadline to get 
doc changes into jdk8. I'll just go ahead with the review now on his 
behalf. I have already review this.

The @FunctionalInterface annotation should to be added to the 
java.util.concurrent.Callable interface, see 
http://mail.openjdk.java.net/pipermail/core-libs-dev/2013-October/022729.html 


diff -r 4d9078b1f25b src/share/classes/java/util/concurrent/Callable.java
--- a/src/share/classes/java/util/concurrent/Callable.java      Tue Nov 
26 14:49:55 2013 +0900
+++ b/src/share/classes/java/util/concurrent/Callable.java      Wed Nov 
27 13:10:39 2013 -0800
@@ -54,6 +54,7 @@
   * @author Doug Lea
   * @param <V> the result type of method {@code call}
   */
+ at FunctionalInterface
  public interface Callable<V> {
      /**
       * Computes a result, or throws an exception if unable to do so.

-Chris.