[horde] Runtime configuration switching

[Lennon Day-Reynolds]

Quoting Jan Schneider <jan at horde.org>:
> [...]
> I thinks it's as easy as right now already. Put Horde outside the
> webroot, add and Alias directive for each vhost, and change or load
> configuration based on SERVER_NAME or HTTP_HOST.
>
> Jan.

Unfortunately, vhost-based switches (while handy) aren't the whole answer. For
instance, our testing and production instances are distinguished only by their
webroot, not their hostname: one is '/horde', and the other is 
'/horde-stage'. This both simplifies our Apache configuration, and 
allows both instances to
share a single SSL cert.

Similarly, my development system is a laptop, and may have 2-3 different IP
addresses and hostnames within a single day as I move from network to network.
Obviously, vhosting is going to fail miserably in that context.

So, a more general top-level config switching mechanism would be greatly
preferable for my needs, at least.

-Lennon