Review Request JDK-8192945: Need stable sort for MODULES entry in the release file

[mandy chung]

The MODULES list in the `release` file is topologically sorted.
For a given module graph, the patch traverses the graph in a
stable order during the topological sort that will produce
the same result for the same module graph.

Webrev at:
http://cr.openjdk.java.net/~mchung/jdk10/webrevs/8192945/webrev.00/

Thanks
Mandy