IndexItem: chain cause to new ClassCastExceptions
CombineAnnotations: fix exception handling

Yes, it is a deprecated class, so not too important, but...
the previous logic felt like bugs crawling all over me.
IndexItem: give more information for all CCEs

It is nice to know the original object type, and the expected target
type, regardless of exactly what went wrong in the adaptation.
IndexItem: report class name upon CCE

It is very, very helpful to know which class has the problematic
annotation index!
Merge pull request #69 from scijava/chain-exceptions

Chain exceptions