go/ast: consider anonymous fields and set Incomplete bit when filtering ASTs
go/ast: consider anonymous fields and set Incomplete bit when filtering ASTs

Also:
- fieldListExports: don't require internal pointer to StructType/InterfaceType node
- filterFieldLists: make structure match fieldListExports

R=rsc
CC=golang-dev
http://codereview.appspot.com/4527050

mhennings/marcohennings-go,Triskite/willstone-goclone,sanjosh/sanjos100-tipc,webfd/go-zh,npe9/noahevans-go9,webfd/go-zh,d0f/go-zh,Triskite/willstone-goclone,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,d0f/go-zh,mhennings/marcohennings-go,bryanxu/go-zh,Triskite/willstone-goclone,Triskite/willstone-goclone,scirelli/scirelli-go,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,scirelli/scirelli-go,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,mhennings/marcohennings-go,mhennings/marcohennings-go,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,glycerine/jeaten-go-arrayof-structof,npe9/noahevans-go9,bryanxu/go-zh,rdp/rogerpack2005-golang,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,webfd/go-zh,rflanagan/reginaldflanagan-project1,bryanxu/go-zh,npe9/noahevans-go9,bryanxu/go-zh,scirelli/scirelli-go,npe9/noahevans-go9,sanjosh/sanjos100-tipc,webfd/go-zh,bryanxu/go-zh,rflanagan/reginaldflanagan-project1,d0f/go-zh,npe9/noahevans-go9,npe9/noahevans-go9,rdp/rogerpack2005-golang,bryanxu/go-zh,webfd/go-zh,webfd/go-zh,d0f/go-zh,bryanxu/go-zh,mhennings/marcohennings-go,rflanagan/reginaldflanagan-project1,sanjosh/sanjos100-tipc,Triskite/willstone-goclone,scirelli/scirelli-go,mhennings/marcohennings-go,bryanxu/go-zh,d0f/go-zh,scirelli/scirelli-go,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,d0f/go-zh,rflanagan/reginaldflanagan-project1,Triskite/willstone-goclone,webfd/go-zh,scirelli/scirelli-go,d0f/go-zh,npe9/noahevans-go9,npe9/noahevans-go9,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,scirelli/scirelli-go,scirelli/scirelli-go,d0f/go-zh