Update of skype expression: make the use of pulse audio optional based on the configuration setting for pulse audio (off by default).

Removing pulse audio from the build inputs when it is not used prevents the bug of Skype taking 100% cpu from showing up.
This demonstrates nicely nix' features: in other distributions the recomended solution was to remove read permission from the
pulse audio libs.

svn path=/nixpkgs/trunk/; revision=31959

pkgs/applications/networking/skype/default.nix

···
 { stdenv, fetchurl, alsaLib, libXv, libXi, libXrender, libXrandr, zlib, glib
 , libXext, libX11, libXScrnSaver, libSM, qt4, libICE, freetype, fontconfig
-, pulseaudio }:
+, pulseaudio, usePulseAudio, lib }:
 
 assert stdenv.system == "i686-linux";
 
···
     sha256 = "157ba3ci12bq0nv2m8wlsab45ib5sccqagyna8nixnhqw9q72sxm";
   };
 
-  buildInputs = [
+  buildInputs = 
+    lib.optional usePulseAudio pulseaudio ++ [
     alsaLib
-    pulseaudio
     stdenv.glibc 
     stdenv.gcc.gcc
     libXv

pkgs/top-level/all-packages.nix

···
     inherit stdenv;
   };
 
+  makeAutostartItem = import ../build-support/make-startupitem {
+    inherit stdenv;
+    inherit lib;
+  };
+
   makeInitrd = {contents}: import ../build-support/kernel/make-initrd.nix {
     inherit stdenv perl cpio contents ubootChooser;
   };
···
 
   alsaUtils = callPackage ../os-specific/linux/alsa-utils { };
 
+  microcodeIntel = callPackage ../os-specific/linux/microcode/intel.nix { };
+
   bcm43xx = callPackage ../os-specific/linux/firmware/bcm43xx { };
 
   bluez = callPackage ../os-specific/linux/bluez { };
···
 
   siproxd = callPackage ../applications/networking/siproxd { };
 
-  skype_linux = callPackage_i686 ../applications/networking/skype { };
+  skype_linux = callPackage_i686 ../applications/networking/skype {
+    usePulseAudio = getConfig [ "pulseaudio" ] false; # disabled by default (the 100% cpu bug)
+  };
 
   slim = callPackage ../applications/display-managers/slim { };