db: Reorganize Berkeley Database Packaging

Currently, the berkeley databases resuses a lot of the same code for the
expressions of each version. This consolidates all of the build routines
similar to that of the linux kernel.

This patch also adds version 6 of BDB.

pkgs/development/libraries/db/generic.nix

@@ -0,0 +1,41 @@
+{ stdenv, fetchurl
+, cxxSupport ? true
+, compat185 ? true
+
+# Options from inherited versions
+, version, sha256
+, extraPatches ? [ ]
+, license ? "Berkeley Database License"
+}:
+
+stdenv.mkDerivation rec {
+  name = "db-${version}";
+
+  src = fetchurl {
+    url = "http://download.oracle.com/berkeley-db/${name}.tar.gz";
+    sha256 = sha256;
+  };
+  
+  patches = extraPatches;
+
+  configureFlags = [
+    (if cxxSupport then "--enable-cxx" else "--disable-cxx")
+    (if compat185 then "--enable-compat185" else "--disable-compat185")
+  ];
+
+  preConfigure = ''
+    cd build_unix
+    configureScript=../dist/configure
+  '';
+
+  postInstall = ''
+    rm -rf $out/docs
+  '';
+
+  meta = with stdenv.lib; {
+    homepage = "http://www.oracle.com/technetwork/database/database-technologies/berkeleydb/index.html";
+    description = "Berkeley DB";
+    license = license;
+    platforms = platforms.unix;
+  };
+}