GROOVY-5709: Improve Grapes error reporting for ZipException

see: https://jira.codehaus.org/browse/GROOVY-5709
GROOVY-5709: Improve Grapes error reporting for ZipException

Incorporated blackdrags feedback by adding the ZipException as the cause to the RuntimeException
Merge pull request #131 from PascalSchumacher/GROOVY-5709

GROOVY-5709: Improve Grapes error reporting for ZipException