Apache 2.4 compatibility

Add netdot_apache24_local.conf which works with Apache 2.4 in Ubuntu 14.04
(note: this requires a version of Apache2::AuthCookie based on the
unreleased httpd24 branch, but Debian have done this)

Fixes redmine #1808
Merge pull request #16 from candlerb/candlerb/1808

Apache 2.4 compatibility