Renamed BDB_ID2ENTRY_PAGESIZE to just BDB_PAGESIZE; set it on each database

instead of just the id2entry db. It helps. I also found that tweaking the
environment (set_lg_bsize 2MB; set_cachesize 2MB) helps but those can be
taken care of in a DB_CONFIG file. Tweaked the bdb_bt_compare function; it
really only needs to be set on little-endian machines. (On big-endian machines
a lexical sort gives the same result as an integer sort.) Moved the final
checkpoint back to the dbenv_close, I think this leaves a cleaner log file.