gobuilder: permit builders of the form goos-goarch-foo
gobuilder: permit builders of the form goos-goarch-foo

R=dfc
CC=golang-dev
http://codereview.appspot.com/4416044

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