Making trac/ldap handle httpd 2.4.

The option authzldapauthoritative had been removed in 2.4

I pushed this into 16.03 instead of master first. My fault.
(cherry picked from commit 516f47efefc44a5465266fe4d72f9136147d2caf)

nixos/modules/services/web-servers/apache-httpd/trac.nix

@@ -5,14 +5,19 @@ with lib;
 let
 
   # Build a Subversion instance with Apache modules and Swig/Python bindings.
-  subversion = pkgs.subversion.override (origArgs: {
+  subversion = pkgs.subversion.override {
     bdbSupport = true;
     httpServer = true;
     pythonBindings = true;
-  });
+    apacheHttpd = httpd;
+  };
 
   pythonLib = p: "${p}/";
 
+  httpd = serverInfo.serverConfig.package;
+
+  versionPre24 = versionOlder httpd.version "2.4";
+
 in
 
 {
@@ -82,7 +87,7 @@ in
         AuthName "${config.ldapAuthentication.name}"
         AuthBasicProvider "ldap"
         AuthLDAPURL "${config.ldapAuthentication.url}"
-        authzldapauthoritative Off
+        ${if versionPre24 then "authzldapauthoritative Off" else ""}
         require valid-user
       </LocationMatch>
     '' else ""}