all-packages: warn when using deprecated attributes

The aliases are split into two groups, as mass-renaming is anticipated.
Also added fold markers as in the rest of file.
https://github.com/NixOS/nixpkgs/issues/9456

pkgs/top-level/all-packages.nix

@@ -15276,8 +15276,13 @@ let
 
   mg = callPackage ../applications/editors/mg { };
 
-
+}
-  # Attributes for backward compatibility.
+  ### Aliases to attributes converted to the dashed-style.
+  // lib.mapAttrs (name: builtins.trace
+    ( "Warning: using a deprecated attribute '${name}'."
+    + " CamelCase and under_scores are replaced by dashed-names"
+    + " to match the nix-env names better."))
+{ # warnings since 2015-09
   adobeReader = adobe-reader;
   arduino_core = arduino-core;  # added 2015-02-04
   asciidocFull = asciidoc-full;  # added 2014-06-22
@@ -15286,8 +15291,6 @@ let
   lttngTools = lttng-tools;  # added 2014-07-31
   lttngUst = lttng-ust;  # added 2014-07-31
   jquery_ui = jquery-ui;  # added 2014-09-07
-  youtubeDL = youtube-dl;  # added 2014-10-26
-  youtube-dl = pythonPackages.youtube-dl; # added 2015-06-07
   rdiff_backup = rdiff-backup;  # added 2014-11-23
   htmlTidy = html-tidy;  # added 2014-12-06
   libtidy = html-tidy;  # added 2014-12-21
@@ -15295,8 +15298,17 @@ let
   sqliteInteractive = sqlite-interactive;  # added 2014-12-06
   nfsUtils = nfs-utils;  # added 2014-12-06
   buildbotSlave = buildbot-slave;  # added 2014-12-09
-  cool-old-term = cool-retro-term; # added 2015-01-31
   rssglx = rss-glx; #added 2015-03-25
+
+}
+  ### Other attribute aliases for backward compatibility.
+  // lib.mapAttrs
+      (name: builtins.trace "Warning: using a deprecated attribute '${name}'.")
+{ # warnings since 2015-09
+  youtubeDL = youtube-dl;  # added 2014-10-26
+  youtube-dl = pythonPackages.youtube-dl; # added 2015-06-07
+  cool-old-term = cool-retro-term; # added 2015-01-31
+
   haskell-ng = haskell;                 # 2015-04-19
   haskellngPackages = haskellPackages;  # 2015-04-19
   inherit (haskell.compiler) jhc uhc;   # 2015-05-15