[tlbuild] xdvi's dependency on libiconv

[Karl Berry]

     # Check whether --with-iconv was given.
    +with_iconv=no

Isn't specifying --without-iconv equivalent?

    I would be grateful if this could be fixed, 

The xdvi configure checks if iconv is available, and uses it if it is.
This seems like correct behavior to me.  The bug seems like having iconv
available in the first place on systems where it is not needed.  Given
that it is erroneously available but undesired, explicitly specifying
--without-iconv seems like the correct approach.

I suppose a more complicated check could be to see if iconv is available
in libc and not look for libiconv if it is in libc.  Or something like
that.  If Paul feels like working on that, more power to him :).

thanks,
karl