[RFC] javadoc: default to not including timestamps

[Benedikt Morbach]

> At Google we also strive for repeatable builds.  We find timestamps
> embedded in jar files to be the biggest problem.
> 
> Timestamps are useful for users checking up-to-dateness via the "Show
> Source" action in a web browser.
Isn't it more useful to just have the version that the docs were built for displayed?
That would be easier to find than having to look at comments in the html source and
"These are the docs for version 1.2" seems more useful than "these docs were built on 2014/07/01"
 
> Making the choice of timestamp explicit in a javadoc invocation seems like
> a good practice.
I'm not quite sure what you are advocating for here :)

> Changing the default behavior is generally not done in the java world
> unless there's a compelling reason.
That's what I feared. Maybe we could add an environment variable to change the default instead?
Though I'm not sure yet how to integrate that over here.