I thought first that the problem was during the execution of
gc.collect(), but its not: when configured --with-pydebug, the exception
is printed before:

>>> import gc, _bsddb; env=_bsddb.DBEnv(3); del env
XXX undetected error
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
bsddb.db.DBNoServerError: (-30992, 'DB_NOSERVER: Fatal error, no RPC
server -- No Berkeley DB RPC server environment')

gc.collect() is just a rude way to display this "XXX undetected error".
(Victor: does Fusil check for this? gc.collect() will not fail if there
is another exception in-between, or in debug mode)

Now, to the _bsddb module: in general, the following pattern is wrong:
   dummy = someFunction();
   Py_XDECREF(dummy);
because it does nothing about an eventual exception set. If the
exception can be discarded, PyErr_Clear() must be called.

I think there is an invariant to keep in each function: return NULL if
and only if an exception is set. Many places in _bsddb do not respect this.