RFR 8020675: invalid jar file in the bootclasspath could lead to jvm fatal error

[Calvin Cheung]

Note that the synopsis of the bug has been changed from:
"Trying to print to a pdf file with PDFill PDF&Image Writer 10.0 Build 4"

bug link: https://bugs.openjdk.java.net/browse/JDK-8020675

I've included the suggestions from Coleen and Ioi in this version of webrev:
     http://cr.openjdk.java.net/~ccheung/8020675/webrev/

Tests:
     jprt
         (in progress - only about 30 tests left on the windows 
platforms, no failure so far;
          a previous run with only Coleen's suggestions was successful)

     vm.quick.testlist on linux_x64

Please review.

thanks,
Calvin