I guess in 1.5.2 a new module, whichdb, was added that attempts to
divine the nature of a database file.  This module doesn't know anything
about Berkeley DB v2 files.  In v2, Sleepycat added a 12-byte null pad
in front of the old magic numbers (at least for hash and btree files).
I've been using v2 for awhile and upgrading to 1.5.2 broke all my
anydbm.open calls. I believe the following patch corrects the problem.