clean files of trailing whitespace

  Trailing whitespace is so unnecessary, that its presence may be
removed before files containing it are distributed.

  Some programs have a tool to point out its presence, like

git
  with option "apply --whitespace=..."

  and in ".git/config": whitespace=...

gcc

  with option "-Wtrailing-whitespace"

grep

  with option -e ' $'

less

  with command "/ $"

mandoc -T lint

  default action

-.-

  An example is the man page "autosp.1".

grep -c -e ' $' reports 77 cases

mandoc -T lint reports 74 cases