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/corefonts/default.nix

@@ -34,18 +34,34 @@ stdenv.mkDerivation {
 
   buildInputs = [cabextract];
 
-  buildCommand = "
+  buildCommand = ''
     for i in $exes; do
         cabextract --lowercase $i
     done
 
     cabextract --lowercase viewer1.cab
-  
+
     fontDir=$out/share/fonts/truetype
     mkdir -p $fontDir
     cp *.ttf $fontDir
 
     # Also put the EULA there to be on the safe side.
     cp ${eula} $fontDir/eula.html
-  ";
+
+    # 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 Andale-Mono Arial-Black Arial Comic-Sans-MS \
+                Courier-New Georgia Impact Times-New-Roman \
+                Trebuchet Verdana Webdings ; do
+      substitute ${./no-op.conf} $out/etc/fonts/conf.d/30-''${name,,}.conf \
+        --subst-var-by fontname "''${name//-/ }"
+    done
+  '';
+
+  meta = {
+    # Set a non-zero priority to allow easy overriding of the
+    # fontconfig configuration files.
+    priority = 5;
+  };
 }