CacheLoader preload should only load as many entries as configured by eviction max entries

This will prevent loading too much into memory causing OOMs, as well as unnecessary eviction thread churn. Probably would require another CacheLoader interface method such as loadAll(int maxEntries). A default version of this method could just call loadAll() and trim the resultset to size, and more sophisticated impls could only load the necessary number of entries, such as a LIMIT SQL query for the JDBC cache stores.