go_spec: fixed a couple omissions/type errors
go_spec: fixed a couple omissions/type errors

- use math.Sqrt instead of Math.sqrt
- use float64 for Point fields to match math.Sqrt
- distinguish between Point and Point3D for clarity
- add alignment sizes for complex types

R=r, rsc, iant, ken2
CC=golang-dev
http://codereview.appspot.com/3420041

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