autoconf-2.13: add versioned executable

Needed by mozilla hg builds.

pkgs/development/tools/misc/autoconf/2.13.nix

@@ -2,7 +2,7 @@
 
 stdenv.mkDerivation rec {
   name = "autoconf-2.13";
-  
+
   src = fetchurl {
     url = "mirror://gnu/autoconf/${name}.tar.gz";
     sha256 = "07krzl4czczdsgzrrw9fiqx35xcf32naf751khg821g5pqv12qgh";
@@ -16,6 +16,8 @@ stdenv.mkDerivation rec {
   # "fixed" path in generated files!
   dontPatchShebangs = true;
 
+  postInstall = ''ln -s autoconf "$out"/bin/autoconf-2.13'';
+
   meta = {
     homepage = http://www.gnu.org/software/autoconf/;
     description = "Part of the GNU Build System";