fakedate(): implement ourselfs (Joseph Bisch)..

fakedate(): implement ourselfs (Joseph Bisch)..

Our fakedate() implementation called ctime(3), but ctime(3) is
implemented by e.g. musl libc via asctime(localtime()) and may
fail, which we did not test.  But it is worse, musl says:

  ISO C requires us to use the above format string,
  even if it will not fit in the buffer. Thus asctime_r
  is _supposed_ to crash if the fields in tm are too large.
  We follow this behavior and crash "gracefully" to warn
  application developers that they may not be so lucky
  on other implementations (e.g. stack smashing..).

so indeed we cannot use ctime() at all, at least for now, since we
get in there for unchecked user dates!  We have to implement that
thing ourselfs for now.