libevent: split into multiple outputs

Hopefully all references are fixed.

pkgs/tools/networking/nylon/default.nix

@@ -1,5 +1,11 @@
-{ stdenv, fetchurl, libevent }:
-
+{ stdenv, fetchurl, libevent, buildEnv }:
+let
+  # failed to find a better way to make it work
+  libevent-comb = buildEnv {
+    inherit (libevent.out) name;
+    paths = [ libevent.dev libevent.out ];
+  };
+in
 stdenv.mkDerivation {
   name = "nylon-1.21";
   src = fetchurl {
@@ -9,7 +15,7 @@ stdenv.mkDerivation {
 
   patches = [ ./configure-use-solib.patch ];
 
-  configureFlags = [ "--with-libevent=${libevent}" ];
+  configureFlags = [ "--with-libevent=${libevent-comb}" ];
 
   buildInputs = [ libevent ];