inconsistency in 4.0k messages

[Göran Uddeborg]

In the help text in 4.0k for "ln" there is a line

"      --target-directory=DIR   move all SOURCE arguments into directory DIR\n"

but the synopsis uses TARGET rather than SOURCE.  SOURCE is used
everywhere else, and TARGET is natural only for (the non-default)
symbolic links.  So maybe it would make sense to use SOURCE in the
synopsis for "ln" too.