Fix the way in which the configure script handles --without-iconv
(and --with-iconv=no), which it used to essentially ignore.
Also fix the way the configure script determines the value of
NEEDS_LIBICONV, which would be incorrectly set to 'YesPlease' on
systems that lack iconv entirely.
Signed-off-by: Marco Nelissen <marcone@xs4all.nl> Signed-off-by: Junio C Hamano <gitster@pobox.com>