O_EXLOCK stuff was introduced in June 1997, and backed out again in
November of that year; however, the corresponding man changes were
never backed out.
do that now, reversing -r1.3 of this file;
original pr and diff from peter philipp (this commit closes pr #4309);
i chose to revert -r1.3 rather than accept the new wording from peter;
thanks jaredy@ for tracking all this down, and supplying the ok...