hg: jdk9/sandbox/langtools: 8176266: Make visitUnknown specification more explicit

[chris.hegarty at oracle.com]

Changeset: 17249d1d92fe
Author:    darcy
Date:      2017-03-07 08:43 -0800
URL:       http://hg.openjdk.java.net/jdk9/sandbox/langtools/rev/17249d1d92fe

8176266: Make visitUnknown specification more explicit
Reviewed-by: jlahoda

! src/java.compiler/share/classes/javax/lang/model/element/ModuleElement.java
! src/java.compiler/share/classes/javax/lang/model/util/AbstractAnnotationValueVisitor6.java
! src/java.compiler/share/classes/javax/lang/model/util/AbstractElementVisitor6.java
! src/java.compiler/share/classes/javax/lang/model/util/AbstractTypeVisitor6.java