This plugin causes all trailing whitespace to be highlighted in red.

To fix the whitespace errors, just call :FixWhitespace.  By default it
operates on the entire file.  Pass a range (or use V to select some lines)
to restrict the portion of the file that gets fixed.

Based on http://vim.wikia.com/wiki/Highlight_unwanted_spaces , and
Thanks to http://github.com/graywh/dotfiles/blob/master/.vimrc#L452
for improving the fix command.