Also, renamed

- noder.lineno -> noder.setlineno (because that's what it does)
- noder.setlineno -> noder.pos    (and return the src.XPos)

Change-Id: I5d3442cf2af97028afcab028290152ce8d062927
Reviewed-on: https://go-review.googlesource.com/c/146317Reviewed-by: Matthew Dempsky <mdempsky@google.com>