[dev] Horde cache driver inconsistence

[Duck]

While reusing horde cached data in an external application I discovered that 
the memcached driver  serialize passed data by its own. But other drivers 
does not. This is a inconsistence between drivers. I guess the driver should 
not serialize passed data since string, boolean ans integer values does not 
need to be serialized. And forcing the driver to serialize you get only 
additional parsing overhead of double (un)serialization.

Duck