crypto/x509: if a parent cert has a raw subject, use it.
crypto/x509: if a parent cert has a raw subject, use it.

This avoids a problem when creating certificates with parents that
were produce by other code: the Go structures don't contain all the
information about the various ASN.1 string types etc and so that
information would otherwise be lost.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/5453067

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