Add cause exception to exceptions created in FieldHandlerImpl getValue()

We recently came across a problem with Castor 1.0.3 where there was an exception during a getValue on a field (due to a remote call). The
exception was printed, but because of the way the IllegalStateExceptions were constructed, we could not get the causing exception (which had data we needed to accurately report the problem).

I would like to propose a simple change: Add the exception to the wrapping IllegalStateException constructed in FieldHandlerImpl.getValue().

I have attached a patch file for just that.

I am using this is my project now, and it behaves as I expect. I can add a specific test case for this if desired.

I will try to put together a simple code sample to produce the problem.