Fix comment to correctly reflect variable used in template.
Remove <IfModule ...> checks as the configuration within the system should be known with respect to the proxy and disk cache modules being loaded. This change also helps because the module name changed in Apache 2.4 from mod_disk_cache to mod_cache_disk, which would have required this template to become more complicated.
Change to determine the $cache_root variable and disk cache module to load depending on the version of Apache. In Apache 2.4 and later the module name changed from mod_disk_cache to mod_cache_disk and so did the location of the cache.

TODO: Determine whether the $cache_root location was also updated in FreeBSD.