If user wants to 'force' a lock, he/she will have to remove the file
manually. some wierd race conditions may happen if different processes optains the
same lock at any given time (thats why lockfile is implemented in the first place)
So lockfile API should not in any circumstances directly provide a way to force taking a lock.
Better to have an destination for every filter then every target.
otherwise one will have to have two targets with the same source but
different destination.
