[Rd] Documentation tweak for ?traceback

[Martin Maechler]

>>>>> brodie gaslam via R-devel 
>>>>>     on Thu, 11 Jul 2019 03:14:53 +0200 writes:

>    The addition of `.traceback` in r70207 adds one more function to the
   > call stack when invoking `traceback()`.  This changes the output of one
   > of the examples to include the error handler call:
   > > options(error = function() traceback(2))
   > > foo(2)
   > [1] 1
   > Error in bar(2) : object 'a.variable.which.does.not.exist' not found
   > 3: (function ()
   >    traceback(2))() at #1
   > 2: bar(2) at #1
   > 1: foo(2)
   > The attached trivial patch cleans up the example so that the above
   > looks like it would have under r<70207.

Indeed, thanks a lot, Brodie!
There was a bit more to change -- the options() setting
is also mentioned in the main text.

Committed to R-devel and R-patched now.

Martin Maechler
ETH Zurich and  R Core Team