Merge staging into closure-size

The most complex problems were from dealing with switches reverted in
the meantime (gcc5, gmp6, ncurses6).
It's likely that darwin is (still) broken nontrivially.

pkgs/development/libraries/ffmpeg/2.6.nix

@@ -1,7 +0,0 @@
-{ callPackage, ... } @ args:
-
-callPackage ./generic.nix (args // rec {
-  version = "${branch}.3";
-  branch = "2.6";
-  sha256 = "1yqc3vm1xrwf866q262qd4nr9d6ifp4gg183pjdc4sl9np0rissr";
-})

pkgs/development/libraries/ffmpeg/2.7.nix

@@ -1,7 +0,0 @@
-{ callPackage, ... } @ args:
-
-callPackage ./generic.nix (args // rec {
-  version = "${branch}.2";
-  branch = "2.7";
-  sha256 = "1wlygd0jp34dk4qagi4h9psn4yk8zgyj7zy9lrpm5332mm87bsvw";
-})

pkgs/development/libraries/ffmpeg/2.8.nix

@@ -0,0 +1,7 @@
+{ callPackage, ... } @ args:
+
+callPackage ./generic.nix (args // rec {
+  version = "${branch}.1";
+  branch = "2.8";
+  sha256 = "1qk6g2h993i0wgs9d2p3ahdc5bqr03mp74bk6r1zj6pfinr5mvg2";
+})

pkgs/development/libraries/ffmpeg/generic.nix

@@ -10,6 +10,8 @@
 , debugDeveloper ? false
 , optimizationsDeveloper ? true
 , extraWarningsDeveloper ? false
+# Darwin frameworks
+, Cocoa
 # Inherit generics
 , branch, sha256, version, ...
 }:
@@ -145,7 +147,8 @@ stdenv.mkDerivation rec {
   ] ++ optional openglSupport mesa
     ++ optionals (!isDarwin) [ libvpx libpulseaudio ] # Need to be fixed on Darwin
     ++ optional (isLinux || isFreeBSD) libva
-    ++ optional isLinux alsaLib;
+    ++ optional isLinux alsaLib
+    ++ optional isDarwin Cocoa;
 
   enableParallelBuilding = true;