[15] RFR: 8248476: No helpful NullPointerException message after calling fillInStackTrace

[Lindenmaier, Goetz]

Hi,

If changing the stack trace by calling fillInStackTrace in user code, the 
NPE algorithm lacks the proper information to compute the message. 
Thus, we must omit it after that call.

I implement this by checking for a call to fillInStackTrace at the bci
recorded in the exception.  
http://cr.openjdk.java.net/~goetz/wr20/8248476-NPE_fillInStackTrace-jdk15/01/

Is there any other way of changing the stack trace?  setStackTrace() is 
no problem as it does not change the internal backtrace datastructure.

I'll push the change to jdk/submit and run it through our CI before pushing.

Best regards,
  Goetz.