gc: allow use of unsafe.Pointer in generated code
gc: allow use of unsafe.Pointer in generated code

The functions we generate to implement == on structs
or arrays may need to refer to unsafe.Pointer even in
safe mode, in order to handle unexported fields contained
in other packages' structs.

R=ken2
CC=golang-dev
http://codereview.appspot.com/5505046

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