Generated key is too long when a QueryKey from StandardQueryCache is used as key

[tedeling]

GeneralDataMemcachedRegion.refineKey does a toString on Hibernate's provided key. This works fine when it's used as 2nd level cache as it's provided a CacheKey object which generates a relatively short toString string.

When used as standard query cache a QueryKey object is provided. The toString of the QueryKey is possibly long as it includes the whole SQL and this is quite often longer than the allowed 250 chars of a Memcached key.

The multitenant issue (#15) is in the same method, will do a PR to fix them both.