AntiCaching Framework Modifications

1.) AntiCacheDB is now a base class for NVMAntiCacheDB and BerkeleyAntiCacheDB.
2.) AntiCacheEvictionManager uses pointers to the base class to manage, so any derived DB can be used.
3.) ExecutionEngine receives a configuration parameter of type AntiCacheDBType to determine which form of AntiCacheDB gets instantiated. 
4.) There is now a configuration parameter hstore_conf.site.anticache_dbtype that defaults to BERKELEY. This is also associated with a Java type AntiCacheDBType.
5.) The configuration parameter is read by ExecutionEngineJNI and passed to the EE there as suggested.
6.) junit tests pass for both anticache_dbtypes BERKELEY and NVM. 
7.) The AntiCacheEvictionManager looks up the blockID in order to find a pointer of the AntiCacheDB instance. It has been discussed changing this to something more efficient, but it should be fine as long as the block count is reasonable.