typing error, causing double flag for pixbuf and missing flag for cover plug-in

--- tumbler-0.1.27/acinclude.m4	2013-01-12 13:14:28.000000000 +0200
+++ tumbler-0.1.27.orig/acinclude.m4	2013-01-13 12:23:46.472324118 +0200
@@ -250,7 +250,7 @@
 dnl
 AC_DEFUN([TUMBLER_COVER_THUMBNAILER],
 [
-AC_ARG_ENABLE([pixbuf-thumbnailer], [AC_HELP_STRING([--disable-cover-thumbnailer], [Don't build the Cover thumbnailer plugin])],
+AC_ARG_ENABLE([cover-thumbnailer], [AC_HELP_STRING([--disable-cover-thumbnailer], [Don't build the Cover thumbnailer plugin])],
   [ac_tumbler_cover_thumbnailer=$enableval], [ac_tumbler_cover_thumbnailer=yes])
 if test x"$ac_tumbler_cover_thumbnailer" = x"yes"; then
   dnl Check for gdk-pixbuf