hg: lambda/lambda/jdk: Clarify that 'accepts a function' means a non-null instance of a functional interface

[brian.goetz at oracle.com]

Changeset: d6db03c537c2
Author:    briangoetz
Date:      2013-10-07 12:56 -0400
URL:       http://hg.openjdk.java.net/lambda/lambda/jdk/rev/d6db03c537c2

Clarify that 'accepts a function' means a non-null instance of a functional interface

! src/share/classes/java/util/function/package-info.java