Update apache.conf files and documentation to use preferred FallbackResource

[stevepiercy]

Retain original mod_rewrite rules for backward compatibility with older versions of Apache.

https://github.com/knop-project/knop/blob/master/knop9/apache/apache.conf
https://github.com/knop-project/knop/blob/master/knop8/apache/apache.conf

Reference:
http://httpd.apache.org/docs/current/rewrite/remapping.html#fallback-resource
Added in version 2.2.16.

http://httpd.apache.org/docs/current/mod/mod_dir.html#fallbackresource
Compatibility: The disabled argument is available in version 2.4.4 and later.