stellarium: build this package on Linux only

Stellarium is supposed to compile on mesaPlatforms, but unfortunately our qt47
expression doesn't support platforms other than Linux.

svn path=/nixpkgs/trunk/; revision=27798

pkgs/applications/science/astronomy/stellarium/default.nix

@@ -25,7 +25,7 @@ stdenv.mkDerivation {
     homepage = http://stellarium.org/;
     license = "GPL2";
 
-    platforms = stdenv.lib.platforms.mesaPlatforms;
+    platforms = stdenv.lib.platforms.linux; # should be mesaPlatforms, but we don't have qt on darwin
     maintainers = [ stdenv.lib.maintainers.simons ];
   };
 }