the configuration object should be checked against the type parameter, as the spycache type doesn't implement the configuration interface.
the specification further defines to throw an exception instead of returning null, but this will be left untouched, as parts of the logic may build upon that null check.
a nulled type argument will return null, to be consistent.
if the client and server do not share a common timezone, e.g amazon cloud, the expiration timestamp might be interpreted differently.
added a pivot time according to the specification of spymemcached (30 days). The exact value will be used if the value is below that threshold, the unix timestamp otherwise, but with the same conditions.
Merge branch 'feature-duration'