The flipside of switching to a new serialization format that, unlike
Java serialization, doesn't store the version in the serialized
representation, is that we need to manage versioning on our own.
Define a version field in PersistentCacheDef, and store this in a new
column in the H2 database. This puts slightly more burden on the cache
implementation to manually manage versions, but makes the process of
updating caches safer; the latter happens much more often than the
former, so the extra up-front effort is worth it.
For existing caches using Java serialization, continue using the default
version of 0. This keeps the same invalidation semantics, and we can
bump the version to 1 when we start implementing new serialization
strategies.
Change-Id: I0d9cccea713fe6dcf368d8b95be59465c336bbb3
49c1c16097