RFR: JDK-8181878: javadoc should support/ignore --add-opens

[Kumar Srinivasan]

Looks good.

Kumar

> Please review a simple change to javadoc, to accept and ignore 
> --add-opens.
> This brings javadoc into line with the module-related options 
> supported by
> java and javac.
>
> The option is simply delegated to javac, for it to handle (ignore) the 
> option.
> Like javac, the option is undocumented/hidden.
>
> Tests are added to ensure that the option is accepted and does not 
> otherwise
> impact javadoc operation.
>
> JBS: https://bugs.openjdk.java.net/browse/JDK-8181878
> Webrev: http://cr.openjdk.java.net/~jjg/8181878/webrev.00/
>
> -- Jon
>