Theo Schlossnagle <email@example.com> 1311893798 -0400
Looks like the dev_t is 4 bytes and the ino_t is 8 leaving
4 bytes of unaligned trash in the jlog_file_id. We were
correctly memsetting the enclosing structure on insertion
into the hash table, but not memsetting the key for lookups
causing a failure to fetch and a subsequent failure to
insert (duplicate). Boom. Nasty.