[Rd] plot.xy() with type="s" and huge data (PR#9629)

[ligges at statistik.uni-dortmund.de]

The following code snippet crashes R (under Windows and Linux) for both 
R-2.4.1 and R-2.5.0 RC as of yesterday:

   set.seed(1)
   H <- rnorm(400000)
   temp <- rnorm(400000)
   plot(H, temp, type='s')
   # (no, it was not my idea to do something like that!)


I *guess* it is some overflow in plot.xy() which calls
   .Internal(plot.xy(xy, type, pch, lty, col, bg, cex, lwd, ...))
but I haven't investigated closely enough, submitting the bug report in 
case anybody can (and has time to) fix this before tomorrow.

Uwe Ligges