Add no-op fontconfig files for Microsoft fonts.

With these fontconfig files it becomes possible for other packages to
configure font aliases for the Microsoft fonts. If both, for example,
vista-fonts and some package providing an alias for Cambria are
installed then the user may control whether or not the alias is active
by manipulating the package priorities.

pkgs/data/fonts/vista-fonts/default.nix

@@ -18,13 +18,26 @@ stdenv.mkDerivation {
   
   buildPhase = "true";
   
-  installPhase = "
-    mkdir -p $out/share/fonts/truetype; cp *.ttf $out/share/fonts/truetype
-  ";
+  installPhase = ''
+    mkdir -p $out/share/fonts/truetype
+    cp *.ttf $out/share/fonts/truetype
+
+    # Set up no-op font configs to override any aliases set up by
+    # other packages.
+    mkdir -p $out/etc/fonts/conf.d
+    for name in Calibri Cambria Candara Consolas Constantia Corbel ; do
+      substitute ${./no-op.conf} $out/etc/fonts/conf.d/30-''${name,,}.conf \
+        --subst-var-by fontname $name
+    done
+  '';
 
   meta = {
     description = "Some TrueType fonts from Microsoft Windows Vista (Calibri, Cambria, Candara, Consolas, Constantia, Corbel)";
     homepage = http://www.microsoft.com/typography/ClearTypeFonts.mspx;
     binaryDistribution = false; # haven't read the EULA, but we probably can't redistribute these files, so...
+
+    # Set a non-zero priority to allow easy overriding of the
+    # fontconfig configuration files.
+    priority = 5;
   };
 }