[Rd] ptr_R_EditFile, R_WriteConsole, and R_ShowMessage

[Thomas Friedrichsmeier]

> R_ShowMessage (ptr_R_ShowMessage):
> This one, too, seems to have very few use-cases (but at least some). Most
> seem to be for errors during startup.
> I wonder:
> 1) If this callback is most useful during startR (...), can it even be used
> in a meaningful way? After all, startR () also initializes all the
> callbacks to the standard values.

Sorry, of course I meant to write Rf_initEmbeddedR (...). I got confused as I 
have this and a few other initialization calls in a functions called startR 
(...).