Better tools for adjusting to strong encapsulation

[mark.reinhold at oracle.com]

Thanks to everyone for all the feedback on this topic.

It appears that issuing warning messages for illegal-access operations
enabled by the precise `--add-opens` and `--add-exports` options is a
bit too aggressive, at least for JDK 9.  Perhaps we can enable that in
JDK 10 after there's been more time for libraries, frameworks, and even
the JDK itself to adjust to the realities of strong encapsulation.

For now I suggest that we revert to the previous behavior of these two
options, so that they do not cause warning messages to be issued.  The
new `--permit-illegal-access` option will continue to generate warning
messages, as proposed.  If those messages are a problem in a particular
scenario then they can be eliminated by switching to an appropriate set
of `--add-opens` options, which can be constructed from the information
contained in those messages.

Comments?

- Mark