path/filepath: add examples for SplitList and Rel.
path/filepath: add examples for SplitList and Rel.

R=golang-dev, bradfitz, minux.ma
CC=golang-dev
https://codereview.appspot.com/7291043

Committer: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,scirelli/scirelli-go,webfd/go-zh,rdp/rogerpack2005-golang,sanjosh/sanjos100-tipc,webfd/go-zh,scirelli/scirelli-go,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,bryanxu/go-zh,mhennings/marcohennings-go,webfd/go-zh,glycerine/jeaten-go-arrayof-structof,rdp/rogerpack2005-golang,scirelli/scirelli-go,webfd/go-zh,d0f/go-zh,mhennings/marcohennings-go,scirelli/scirelli-go,scirelli/scirelli-go,rdp/rogerpack2005-golang,scirelli/scirelli-go,bryanxu/go-zh,d0f/go-zh,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,bryanxu/go-zh,sanjosh/sanjos100-tipc,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,mhennings/marcohennings-go,mhennings/marcohennings-go,glycerine/jeaten-go-arrayof-structof,mhennings/marcohennings-go,sanjosh/sanjos100-tipc,sanjosh/sanjos100-tipc,webfd/go-zh,rdp/rogerpack2005-golang,rdp/rogerpack2005-golang,bryanxu/go-zh,bryanxu/go-zh,d0f/go-zh,scirelli/scirelli-go,webfd/go-zh,d0f/go-zh,d0f/go-zh,mhennings/marcohennings-go,rdp/rogerpack2005-golang,glycerine/jeaten-go-arrayof-structof,sanjosh/sanjos100-tipc,d0f/go-zh,scirelli/scirelli-go,bryanxu/go-zh,mhennings/marcohennings-go,webfd/go-zh,rdp/rogerpack2005-golang,bryanxu/go-zh,sanjosh/sanjos100-tipc,webfd/go-zh,d0f/go-zh,d0f/go-zh,bryanxu/go-zh