Don't generate NameVirtualHost directives for v2.4.

The NameVirtualHost directive has been deprecated since version 2.3.11
of httpd; now name-based virtual hosting is automatically enabled for
any IP/port combination used in more than one <VirtualHost> directive.
NameVirtualHost is now a no-op, but gives a warning on startup, so
don't generate those directives when running newer versions of httpd.

templates/named_vhost.conf.erb

 <%
+    httpd_version = scope.lookupvar('apache::standard_version')
+
     server_names = []
     server_addrs = []
     [@urls].flatten.sort.each do |u|
@@ -57,8 +59,12 @@
 ##	cfg << 'DocumentRoot ' + @documentroot
 ##    end
 -%>
-<% server_addrs.each do |addr| -%>
+<% if (httpd_version  and  httpd_version != ''  and
+       scope.function_versioncmp([httpd_version, '2.3.11']) < 0)
+      server_addrs.each do |addr|
+-%>
 NameVirtualHost <%= addr %>
+<%    end -%>
 <% end -%>
 <VirtualHost <%= server_addrs.join(' ') %>>