[R] R still accepts the undocumented option --with-iconv=no

[Dr. David Kirkby]

This is not so much a user help question, as a bug report (I think!)

Previous versions of R allowed the option --with-iconv=no to used to disable the 
use of iconv. That option is no longer documented. However, using that option on 
the latest does not generate an error message, but is silently ignored. Later 
one gets the message:

configure: error: a suitable iconv is essential

So since it is essential to have iconv package, it is desirable to have the 
option rejected.

Dave