caffeine-ng: add missing dependencies, fix bin paths

pkgs/tools/X11/caffeine-ng/default.nix

@@ -1,5 +1,5 @@
 { gdk-pixbuf, glib, gobject-introspection, gtk3, lib, libnotify,
-  python3Packages, wrapGAppsHook
+  procps, xset, xautolock, xscreensaver, python3Packages, wrapGAppsHook
 }:
 
 python3Packages.buildPythonApplication rec {
@@ -23,6 +23,14 @@ python3Packages.buildPythonApplication rec {
 
   doCheck = false; # There are no tests.
 
+  postPatch = ''
+    substituteInPlace caffeine/inhibitors.py \
+      --replace 'os.system("xset' 'os.system("${xset}/bin/xset' \
+      --replace 'os.system("xautolock' 'os.system("${xautolock}/bin/xautolock' \
+      --replace 'os.system("pgrep' 'os.system("${procps}/bin/pgrep' \
+      --replace 'os.system("xscreensaver-command' 'os.system("${xscreensaver}/bin/xscreensaver-command'
+  '';
+
   postInstall = ''
     mkdir -p $out/share
     cp -r share $out/