Check unsupported tag number
Check unsupported tag number

Re-apply the following commit, accidentally removed by
8cd05358cbb166895dcdb71633078552a8af82cd.

commit 64ee4180ddd1dfda5a45a5c7e8752622d6f09dd3
Author: Hiroshi Nakamura <nahi@ruby-lang.org>
Date:   Mon Jan 30 22:55:57 2012 +0900

    Check unsupported tag number

emboss/krypt-core-c,emboss/krypt-core-c