freetype+fontconfig: add infinality and enable it

Also add fontconfig checks
, change license to "unfree" if using patented code.

Inspired by Corey O'Connor in #89
https://github.com/coreyoconnor/nixpkgs/commit/27fec0aa26d44716134a86efaf48209be7c46138

pkgs/development/libraries/fontconfig/default.nix

@@ -8,6 +8,13 @@ stdenv.mkDerivation rec {
     sha256 = "0llraqw86jmw4vzv7inskp3xxm2gc64my08iwq5mzncgfdbfza4f";
   };
 
+  infinality_patch = with freetype.infinality; if useInfinality
+    then let subvers = "1";
+      in fetchurl {
+        url = "${base_URL}/fontconfig-infinality-1-${vers}_${subvers}.tar.bz2";
+        sha256 = "1fm5xx0mx2243jrq5rxk4v0ajw2nawpj23399h710bx6hd1rviq7";
+      }
+    else null;
 
   buildInputs = [ pkgconfig freetype expat ];
 
@@ -29,6 +36,10 @@ stdenv.mkDerivation rec {
   # Don't try to write to /etc/fonts or /var/cache/fontconfig at install time.
   installFlags = "CONFDIR=$(out)/etc/fonts RUN_FC_CACHE_TEST=false fc_cachedir=$(TMPDIR)/dummy";
 
+  postInstall = if !freetype.infinality.useInfinality then "" else ''
+    cd "$out/etc/fonts" && tar xvf ${infinality_patch}
+  '';
+
   meta = {
     description = "A library for font customization and configuration";
     homepage = http://fontconfig.org/;