Revert "Remove kde4.psi"

This reverts commit c2fcc909cb42d9aaa456d211f9c68cc24f4ef804.

- Upstream development is ongoing; we will keep psi for now to preserve
  continuity.

pkgs/applications/networking/instant-messengers/psi/default.nix

@@ -0,0 +1,30 @@
+{ stdenv, fetchurl, enchant, qt4, zlib, sox, libX11, xproto, libSM
+, libICE, qca2, pkgconfig, callPackage, which, glib
+, libXScrnSaver, scrnsaverproto
+}:
+
+stdenv.mkDerivation rec {
+  name = "psi-0.15";
+
+  src = fetchurl {
+    url = "mirror://sourceforge/psi/${name}.tar.bz2";
+    sha256 = "593b5ddd7934af69c245afb0e7290047fd7dedcfd8765baca5a3a024c569c7e6";
+  };
+
+  buildInputs =
+    [ enchant qt4 zlib sox libX11 xproto libSM libICE
+      qca2 pkgconfig which glib scrnsaverproto libXScrnSaver
+    ];
+
+  NIX_CFLAGS_COMPILE="-I${qca2}/include/QtCrypto";
+
+  NIX_LDFLAGS="-lqca";
+
+  enableParallelBuilding = true;
+
+  meta = {
+    description = "Psi, an XMPP (Jabber) client";
+    maintainers = [ stdenv.lib.maintainers.raskin ];
+    platforms = stdenv.lib.platforms.linux;
+  };
+}

pkgs/top-level/all-packages.nix

@@ -16720,6 +16720,7 @@ with pkgs;
         krusader = callPackage ../applications/misc/krusader { };
 
         massif-visualizer = callPackage ../development/tools/analysis/massif-visualizer { };
+        psi = callPackage ../applications/networking/instant-messengers/psi { };
 
         telepathy = callPackage ../applications/networking/instant-messengers/telepathy/kde {};