RFR(s): 8217405 rmic should reject class files with preview features enabled

[Stuart Marks]

Hi all,

Please review this small fix to rmic to make it reject class files that were 
compiled with preview features enabled.

Bug:

	https://bugs.openjdk.java.net/browse/JDK-8217405

Webrev:

	http://cr.openjdk.java.net/~smarks/reviews/8217405/webrev.0/

Note that there is no regression test with this patch; I've added the noreg-hard 
label. The main reason is that to test this properly requires multiple different 
JDK versions to be available simultaneously, which isn't supported in out the 
test environment. One could work around this, e.g. by constructing class files 
with the desired version information, from but this hardly seems worth it for 
something like rmic.

Thanks,

s'marks