Code review request for SecurityManager changes

[Sean Mullan]

See 
http://cr.openjdk.java.net/~mullan/jigsaw/webrevs/SecurityManager/webrev.00/ 
for an initial set of changes to allow modules to be run with a 
SecurityManager.

ModuleClassLoader now extends SecureClassLoader.

There is no CodeSigner support yet. That will be coming later after we 
integrate signed modules.

Thanks,
Sean