Fix bug in godoc tab conversion filter: tabs after an empty line where not converted.
Fix bug in godoc tab conversion filter:
tabs after an empty line where not converted.

Also, made it more robust in the presence of
(unexpected) ' ' and '\v' chars in indentation
mode.

R=r
CC=golang-dev
http://codereview.appspot.com/181085

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