crypto/rsa: add SHA-224 hash prefix
crypto/rsa: add SHA-224 hash prefix

http://www.rsa.com/rsalabs/node.asp?id=2125:

NOTE: A new OID has been defined for the combination
of the v1.5 signature scheme and the SHA-224 hash function:
        sha224WithRSAEncryption OBJECT IDENTIFIER ::=
Like the other sha*WithRSAEncryption OIDs in PKCS #1 v2.1,
this OID has NULL parameters.
The DigestInfo encoding for SHA-224 (see Section 9.2, Note 1) is:
        (0x)30 2d 30 0d 06 09 60 86 48 01 65 03 04 02 04 05 00 04 1c || H

R=golang-dev, agl
CC=golang-dev
http://codereview.appspot.com/6208076

bryanxu/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,rdp/rogerpack2005-golang,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,bryanxu/go-zh,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,d0f/go-zh,Triskite/willstone-goclone,rdp/rogerpack2005-golang,bryanxu/go-zh,webfd/go-zh,bryanxu/go-zh,sanjosh/sanjos100-tipc,d0f/go-zh,d0f/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,d0f/go-zh,mhennings/marcohennings-go,bryanxu/go-zh,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,scirelli/scirelli-go,Triskite/willstone-goclone,mhennings/marcohennings-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,rflanagan/reginaldflanagan-project1,mhennings/marcohennings-go,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,webfd/go-zh,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,d0f/go-zh,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,bryanxu/go-zh,rdp/rogerpack2005-golang,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,Triskite/willstone-goclone,scirelli/scirelli-go,webfd/go-zh,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,rdp/rogerpack2005-golang,webfd/go-zh,webfd/go-zh,scirelli/scirelli-go,d0f/go-zh,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,bryanxu/go-zh,webfd/go-zh,sanjosh/sanjos100-tipc,bryanxu/go-zh,Triskite/willstone-goclone,scirelli/scirelli-go,scirelli/scirelli-go