* Converts error_directory squid.conf option into an optional override.
Providing backward compatibility with older configurations and local
customizations.
* Adds error_default_language to administratively set the backup
language presented by Squid.
* Fixes design of previously broken hard-coded failover language.
WAS: default to FreeBSD error install location. Hidden by
error_directory being required.
NOW: failover to build-time configured errors/ directory 'English'
templates.
* Adds --enable-auto-locale configure option to enable the following.
* Adds logic to locate visitors most-preferred of available languages
and present a tailored error page as their reply.