Sigtest should generate java.lang.ClassFormatError exception if classfile can't be read

Could you please throw only java.lang.ClassFormatError when classfile is invalid,
it is easier than update apiCover.

To check this it is possible to generate coverage for vm.classfmt tests.
TCK=/set/java/re/jck/6b/nightly/binaries/latest/JCK-runtime-6b/classes
#TCK=/java/re/jck/6/archive/fcs/binaries/JCK-runtime-6/classes


java -Xmx512m -cp apiCover.jar:sigtestdev.jar com.sun.tdk.apiCover.Main \
-api j2se60_all.sig -tck $TCK \
-apiinclude java.lang.Object \
-tckinclude javasoft.sqe.tests.vm.classfmt \
-tckinclude javasoft.sqe.tests.vm.concepts \
-debug -mode r -detail 1 -report res.txt