Review Request: JDK-8173374: Update GenGraphs tool to generate dot graph with requires transitive edges

[Mandy Chung]

> On Feb 15, 2017, at 12:27 PM, Daniel Fuchs <daniel.fuchs at oracle.com> wrote:
> 
> Hi Mandy,
> 
> > Updated webrev:
> >   http://cr.openjdk.java.net/~mchung/jdk9/webrevs/8173374/webrev.01/
> 
> Looks good. I haven't reviewed the build changes.
> I assume they're OK if you managed to build ;-)

Thanks.  

The build change is trivial adding —-add-exports for compiling and running GenGraphs build tool.  Also add a new target to generate spec-only module graphs.

Mandy