make configure --whatever --help work as expected

Originally committed as revision 5434 to svn://svn.ffmpeg.org/ffmpeg/trunk

configure

@@ -3,13 +3,10 @@
 # ffmpeg configure script (c) 2000, 2001, 2002 Fabrice Bellard
 #
 
-if test x"$1" = x"-h" -o x"$1" = x"--help" ; then
-cat << EOF
-
-Usage: configure [options]
-Options: [defaults in brackets after descriptions]
-
-EOF
+show_help(){
+  echo "Usage: configure [options]"
+  echo "Options: [defaults in brackets after descriptions]"
+  echo
   echo "Standard options:"
   echo "  --help                   print this message"
   echo "  --prefix=PREFIX          install in PREFIX [$prefix]"
@@ -97,6 +94,10 @@ echo "  --disable-demuxers       disables all demuxers"
   echo ""
   echo "NOTE: Object files are built at the place where configure is launched."
   exit 1
+}
+
+if test x"$1" = x"-h" -o x"$1" = x"--help" ; then
+    show_help
 fi
 
 # set temporary file name
@@ -622,6 +623,8 @@ for opt do
   ;;
   --disable-demuxers) demuxers="no"
   ;;
+  --help) show_help
+  ;;
   *)
   echo "Unknown option \"$opt\"."
   echo "See $0 --help for available options."