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

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang