hg: jdk/sandbox: 8199196: Add javadoc support for preview features

[chris.hegarty at oracle.com]

Changeset: 0b63526d1550
Author:    jjg
Date:      2018-05-08 12:16 -0700
URL:       http://hg.openjdk.java.net/jdk/sandbox/rev/0b63526d1550

8199196: Add javadoc support for preview features
Reviewed-by: ksrini

! src/jdk.javadoc/share/classes/jdk/javadoc/internal/tool/ToolOption.java
! src/jdk.javadoc/share/classes/jdk/javadoc/internal/tool/resources/javadoc.properties
+ test/langtools/jdk/javadoc/tool/EnablePreviewOption.java