Fix:

[weli@dhcp-66-78-87 httpd24-jws3-el7]$ git diff
diff --git a/00-base.conf b/00-base.conf
index 1af899e..83f741c 100644
--- a/00-base.conf
+++ b/00-base.conf
@@ -65,7 +65,7 @@ LoadModule vhost_alias_module modules/mod_vhost_alias.so
 #LoadModule watchdog_module modules/mod_watchdog.so
 #LoadModule heartbeat_module modules/mod_heartbeat.so
 #LoadModule heartmonitor_module modules/mod_heartmonitor.so
-#LoadModule usertrack_module modules/mod_usertrack.so
+LoadModule usertrack_module modules/mod_usertrack.so
 #LoadModule dialup_module modules/mod_dialup.so
 #LoadModule charset_lite_module modules/mod_charset_lite.so
 #LoadModule log_debug_module modules/mod_log_debug.so

Verification:

[weli@dhcp-66-78-87 sbin]$ ./apachectl -M | grep usertrack
 usertrack_module (shared)

Sample config for testing:

LogFormat "%{Apache}n %r %t" usertrack
CustomLog logs/clickstream.log usertrack

Result:

[weli@dhcp-66-78-87 sbin]$ curl http://localhost
ok.
[weli@dhcp-66-78-87 sbin]$ ls ../logs/
access_log  clickstream.log  error_log  httpd.log  ssl_access_log  ssl_error_log  ssl_request_log
[weli@dhcp-66-78-87 sbin]$ cat ../logs/clickstream.log
- GET / HTTP/1.1 [26/Jan/2015:17:17:16 +0800]

Verified with DR2 RHEL6 RHEL7 zips.