pkgs/top-level/all-packages.nix, pkgs/tools/networking/openssh: prefer makeOverridable over getPkgConfig to customize openssh

Changed 'openssh' expression to allow for argument overriding instead of
relying on getPkgConfig. While I was at it, I also simplified the build
expression a bit.

svn path=/nixpkgs/trunk/; revision=21868

pkgs/tools/networking/openssh/default.nix

@@ -1,11 +1,8 @@
-{ stdenv, fetchurl, zlib, openssl, perl, libedit, pkgconfig
-, pamSupport ? false, pam ? null
+{ stdenv, fetchurl, zlib, openssl, perl, libedit, pkgconfig, pam
 , etcDir ? null
 , hpnSupport ? false
 }:
 
-assert pamSupport -> pam != null;
-
 let
 
   hpnSrc = fetchurl {
@@ -28,16 +25,14 @@ stdenv.mkDerivation rec {
       gunzip -c ${hpnSrc} | patch -p1
     '';
   patches = [ ./locale_archive.patch ];
-  
-  buildInputs =
-    [ zlib openssl perl libedit pkgconfig ]
-    ++ stdenv.lib.optional pamSupport pam;
+
+  buildInputs = [ zlib openssl perl libedit pkgconfig pam ];
 
   configureFlags =
     ''
       --with-mantype=man
       --with-libedit=yes
-      ${if pamSupport then "--with-pam" else "--without-pam"}
+      ${if pam != null then "--with-pam" else "--without-pam"}
       ${if etcDir != null then "--sysconfdir=${etcDir}" else ""}
     '';