8173393: Module system implementation refresh (2/2017)
Reviewed-by: lfoltan, acorn, mchung
Contributed-by: alan.bateman@oracle.com, george.triantafillou@oracle.com

8159262: Walking PackageEntry Export and ModuleEntry Reads Must Occur Only When Neccessary And Wait Until ClassLoader's Aliveness Determined
Summary: Fixed an issue in class unloading to delay walk until class loader's aliveness is determined of modularity lists to remove dead modules
Reviewed-by: coleenp, dholmes, sspitsyn, zgu