It might seem strange, but somehow my .vimrc file wasn’t version controlled so when I wiped my machine, I had to dig up the settings one can/should use for making tabs become spaces, 4 spaces. So here it is:
" http://stackoverflow.com/questions/1878974/redefine-tab-as-4-spaces
" size of a hard tabstop
set tabstop=4
" size of an "indent"
set shiftwidth=4
" a combination of spaces and tabs are used to simulate tab stops at a width other than the (hard)tabstop
set softtabstop=4
" make "tab" insert indents instead of tabs at the beginning of a line
set smarttab
" always uses spaces instead of tab characters
set expandtab
Once set :retab is a good command to “fix it”. :-)