[Rd] segfault in plot(x, y, col = aFactor) (PR#9221)

[maechler at stat.math.ethz.ch]

Thank you, Bjørn-Helge.
A shorter version is
   plot(1:500, col = gl(2,250))

Interestingly, with much shorter vectors of length (n), the correct warning
is produced (n times).
And once that has happened, you can use longer vectors without
any problem.

As you said  ``issued just after starting R''
seems quite relevant.

When run in 'R -d gdb', the backtrace ("bt") seems to indicate
that the problem is happening during the  (C-level) warning() call.

Martin