[Rd] model.frame problem

[Terry Therneau]

 A few weeks ago I reported a problem with model.frame, whose root lay
in a formula expression "....+ ratetable(x1=x1, x2=x2, ....x100=x100)"
that was really long and caused model.frame to fail.  Brian had some
indefinite ideas on what might need to change in the base code to handle
it.

  In survival_2.36-1 the bit of code that generated the offending
expression has been changed (mostly for other reasons).  The problem
case in question no longer is generated.  If fixing this issue was on
anyone's list of things to do, feel free to drop the priority to zero. 
(You could still generate this with just exactly the right call to
pyears, but I'll be boarding up that final door in 2.36-2.)

Terry Therneau