Support Gnuk Token

Hello,

Here is my patch to support Gnuk Token (http://www.fsij.org/gnuk/), which is based on OpenPGP v2 but with some differences.

##### Features enabled:
- All operations done on CryptoStick can be done with Gnuk:
    + Read, write DOs.
    + Generate and import key. Import key & certificate. However, Gnuk only support 2048-bit key length.
    + Authenticate, sign email, decrypt email with certificate.
- New for CryptoStick:
    + Erase card.
- For Gnuk only:
    + Delete key.

##### Evidence:
- Log for openpgp-tool:
    + Generate key: http://pastebin.com/8khZ5Vjz
    + Delete key: http://pastebin.com/4Yap2HEw
- Log for pkcs15-init:
    + Import key & certificate http://pastebin.com/GMV2Ec6f
(there is also log from pkcs11-tool to list objects before and after importing)
- Screenshots for Thunderbird use:
    + http://storage7.static.itmages.com/i/13/0412/h_1365763587_3501335_8b4c8c4809.png
   + http://storage8.static.itmages.com/i/13/0412/h_1365763655_7634824_df90addc99.png
   + http://storage9.static.itmages.com/i/13/0412/h_1365763672_1347044_0d3449da2b.png