just add comments about outputs (cups, gdk-pixbuf)

pkgs/development/libraries/gdk-pixbuf/default.nix

@@ -33,7 +33,7 @@ stdenv.mkDerivation rec {
   # The tests take an excessive amount of time (> 1.5 hours) and memory (> 6 GB).
   inherit (doCheck);
 
-  # propagate the bin output
+  # propagate the bin output TODO: use propagatedOutputs instead
   postPhases = "postPostFixup";
   postPostFixup = ''
     echo -n " $bin" >> "$dev"/nix-support/propagated-*build-inputs

pkgs/misc/cups/default.nix

@@ -17,7 +17,7 @@ stdenv.mkDerivation {
   };
 
   # FIXME: the cups libraries contains some $out/share strings so can't be split.
-  outputs = [ "dev" "out" "doc" "man" ];
+  outputs = [ "dev" "out" "doc" "man" ]; # TODO: above
 
   buildInputs = [ pkgconfig zlib libjpeg libpng libtiff libusb gnutls avahi libpaper ]
     ++ optionals stdenv.isLinux [ pam dbus.libs acl ];