Previously a purge_store was only purging caches but it was leaving a
reference to the store instance for the cache definition.
As a result, the cache was never cleared away correctly and, in cases
where the cache store makes a TCP connection to a backend system, the
number of open sockets was increasing for each store instance.
After a complete purge, as found in the unit test reset, the cache
definitions should be both purged and removed.
This change should also lead to a drop in memory consumption for unit
tests as there will no longer be references to unused definition stores.
Andrew Nicols
c5dd7b71da