fix handling of iconv configuration options

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>

Author: Marco Nelissen

configure.ac

@@ -385,6 +385,8 @@ AC_SUBST(NO_EXPAT)
 # some Solaris installations).
 # Define NO_ICONV if neither libc nor libiconv support iconv.
 
+if test -z "$NO_ICONV"; then
+
 GIT_STASH_FLAGS($ICONVDIR)
 
 AC_DEFUN([ICONVTEST_SRC], [
@@ -431,6 +433,12 @@ GIT_UNSTASH_FLAGS($ICONVDIR)
 AC_SUBST(NEEDS_LIBICONV)
 AC_SUBST(NO_ICONV)
 
+if test -n "$NO_ICONV"; then
+    NEEDS_LIBICONV=
+fi
+
+fi
+
 #
 # Define NO_DEFLATE_BOUND if deflateBound is missing from zlib.