RFR: 8047373: Clean the ExceptionCache in one pass

[Stefan Karlsson]

Hi all,

Please, review this patch to clean the ExceptionCache in one pass, 
instead of re-searching for the element to remove. The patch also makes 
nmethod::do_unloading little bit easier to read, IMHO.

http://cr.openjdk.java.net/~stefank/8047373/webrev.00
https://bugs.openjdk.java.net/browse/JDK-8047373

This patch has been used and tested in the G1 Class Unloading project.

thanks,
StefanK