cmd/go: fix 'go help' It depended on old behavior of functions in structs. Solved by adding a boolean method to check .Run != nil.
cmd/go: fix 'go help'
It depended on old behavior of functions in structs.
Solved by adding a boolean method to check .Run != nil.

R=golang-dev, adg, r, rsc
CC=golang-dev
http://codereview.appspot.com/5674062

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