[Rd] ask.yes.no() function

[Duncan Murdoch]

As described in 
<https://bugs.r-project.org/bugzilla3/show_bug.cgi?id=17242>, R base 
functions are currently inconsistent in asking interactive "yes/no" type 
questions.  One solution to this is to have a function to do it, and to 
use it consistently.

Rather than just writing such a function and possibly missing some 
desirable feature, I'd like to ask if anyone can point to an existing 
one that is perfect (or nearly perfect, and point out what changes would 
be desirable)?

Duncan Murdoch