added PluginErrorException and its handling to PluginTask
removed unnecessary import
replaced DuplicatedClassFileException with DuplicatedClassFileError and used it with PluginErrorException
got rid of DuplicatePathInJarException, IllegalPathInJarException, appropriate errors are reported by throwing PluginErrorException
got rid of DuplicatePathInZipException, IllegalPathInZipException, appropriate errors are reported by throwing PluginErrorException
renamed class names DuplicatedXxx to DuplicateXxx