return "unknown error" instead of NULL in verror_get_string() if there is no error stored, so callers don't have to check for NULL returns
return "unknown error" instead of NULL in verror_get_string() if there is
no error stored, so callers don't have to check for NULL returns

ellert/globus-toolkit,ellert/globus-toolkit,gridcf/gct,globus/globus-toolkit,gridcf/gct,ellert/globus-toolkit,globus/globus-toolkit,gridcf/gct,globus/globus-toolkit,gridcf/gct,ellert/globus-toolkit,globus/globus-toolkit,globus/globus-toolkit,ellert/globus-toolkit,ellert/globus-toolkit,globus/globus-toolkit,gridcf/gct,ellert/globus-toolkit,gridcf/gct,globus/globus-toolkit,ellert/globus-toolkit,globus/globus-toolkit