autoheader typo: --warnings, not --warning

[Paul Eggert]

I got this fix from:
http://ftp.debian.org/debian/pool/main/a/autoconf/autoconf_2.53-5.diff.gz

2002-09-01  Paul Eggert  <address@hidden>

        * bin/autoheader.in (parse_args): --warning -> --warnings.

--- bin/autoheader.in.~1.120.~  2002-07-17 01:30:43.000000000 -0700
+++ bin/autoheader.in   2002-09-01 04:01:17.900321000 -0700
@@ -106,7 +106,7 @@ sub parse_args ()
 
   getopt ('I|include|A|autoconf-dir|m|macrodir|l|localdir=s' => address@hidden,
          'B|prepend-include=s' => address@hidden,
-         'W|warning=s' => address@hidden);
+         'W|warnings=s' => address@hidden);
 
   if (! @ARGV)
     {