[horde] Can't upgrade Horde_Memcache

[Brent]

  Quoting Jens Wahnes <wahnes at uni-koeln.de>:

> Brent wrote:
>> My horde installation WAS working with pecl memcache, but I just  
>> removed it and installed pecl memcached instead and now I can  
>> upgrade Horde/Memcache.
>
> I agree that it's pretty confusing to have two competing PHP/PECL  
> packages like memcache and memcached that do the same thing for the  
> most, but differ in subtleties.  I've been sticking with the  
> memcached package for a while now and it seems to work OK.
>
>> Seems to be working; though, I've no idea how to test whatever this  
>> module does directly.  I can only say that horde seems to be  
>> working, but it is caching anything?  No clue.
>
> You can run the "horde-memcache-stats" tool to show you some stats  
> about cache usage.  If the figures reported there increase over  
> time, as users access common data within Horde, you can be pretty  
> sure that the cache is actually being used.
>
> Jens
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Hmm...well:

$ horde-memcache-stats
  Fatal Error:
  Memcache HashTable driver not enabled.

  1. Horde_Cli->fatal() /usr/bin/horde-memcache-stats:32

I seem to have caching turned on in Settings>Horde>Caching.

* $conf[cache][default_lifetime] = 8640
* $conf[cache][driver] = Store data in filesystem
$conf[cache][params][dir] = /var/lib/php/session
...
* $conf[cache][use_memorycache] = None

I do have files in /var/lib/php/session/* that start with cache_,  
about 2900 of them.  I tried changing the last option from None to the  
available options and I still get "HashTable driver not enabled".  I'm  
unclear where this setting might be located.

Thanks!