spec: function invocation, panic on *nil Document that indirection through a nil pointer will panic. Explain function invocation. This section will need more work, but it's a start.
spec: function invocation, panic on *nil
Document that indirection through a nil pointer will panic.
Explain function invocation.
This section will need more work, but it's a start.

Fixes issue 1865.
Fixes issue 2252.

R=rsc, iant, r
CC=golang-dev
http://codereview.appspot.com/5532114

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