Add mapping or function for sudo tee write to read only file trick

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See :SudoWrite from https://github.com/tpope/vim-eunuch as one possiblility

for more information about the sudo tee trick see http://www.geekyboy.com/archives/629

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" :W sudo saves the file 
" (useful for handling the permission-denied error)
command W w !sudo tee % > /dev/null

from amix/vimrc

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or

" Allow saving of files as sudo when I forgot to start vim using sudo.
cmap w!! w !sudo tee > /dev/null %

We had this previously but we had the % before the >, I'm not sure why this removed (or if if also gives the correct behavior).

See this explanation of why this works