Upgrade tasks do not flush the cache after updating content

In the case where the content of a table is updated, the second-level cache is not flushed after the task has completed. This can lead to unpredictable errors in the use of the system, until it is shut down (and the cache rebuilt when Confluence starts up again).

One such issue (CONF-4765) is where the SPACEDESCRIPTION objects in the CONTENT table were updated to reflect a change made somewhere around 1.3.5. Without this change, the space key for a Space Description object would be null. Although the record was updated in the database, the second-level cache (CacheManager) did not reflect this change, and so errors would occur when dealing with the Space Description until a restart.