RFR: 8151832: Improve exception messages in exceptions thrown by jigsaw code

[Seán Coffey]

Some extra capturing of context in exception handling. I've re-based the 
original suggested patch and added some minor edits.

https://bugs.openjdk.java.net/browse/JDK-8151832
webrev : 
http://cr.openjdk.java.net/~coffeys/webrev.8151832/webrev/index.html

-- 
Regards,
Sean.