RFR 8176147: JVM should throw CFE for duplicate Signature attributes

[harold seigel]

Hi,

Please review this JDK-9 fix to throw a ClassFormatError exception if 
the attributes table for a class, field, or method contains more than 
one Signature attribute.

Open webrev: http://cr.openjdk.java.net/~hseigel/bug_8176147/webrev/

JBS Bug: https://bugs.openjdk.java.net/browse/JDK-8176147

The fix was tested with the JCK lang and vm tests, the JTreg hotspot, 
java/io, java/lang, java/util and other tests, the RBT tier2 -tier5 
tests, the colocated and non-colocated NSK tests, and with JPRT.

Thanks, Harold