This plugin causes trailing whitespace to be highlighted in red.
To fix the whitespace errors, 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.
The repo is at http://github.com/bronson/vim-trailing-whitespace
Originally based on http://vim.wikia.com/wiki/Highlight_unwanted_spaces
License: cc-by-sa. The instructions this plugin is based on were licensed cc-by-sa so, until a reason to force a different license appears, we'll continue to use it.
A more complete alternative is at https://github.com/ntpeters/vim-better-whitespace