DefaultMethodReturnInformation handles exceptions in some cases not correctly

[Frederik Buss-Joraschek]

Getting all occured exceptions with

      _throwInstructions.toSeq.map(result.operandsArray(_).head)

fails, when the exception is not created in the code. All exceptions created by the domain, such like NullPointerExceptions from a ArrayValues implementation, will cause a non exceptions value to be part of the list.

[Michael Eichberg]

fixed by commit https://bitbucket.org/delors/opal/commits/258548e21730db6d16e4f543bcc7bf815b684914