I keep forgetting that PyDict_GetItem has it's own special
refcount rules.

dropped from the cache.

ExtensionClass deletion protocol.

Added DECREF for object id, which is now an object.

destination version to fail to detect the new data.

invalidated objects.

Waaa.  I'll probably need to add a separate lock file.

methods did setattrs.

tries to minimize the size of the cache.

"volatile" attributes (starting with _v_) to cause database writes.

class, we save the class mosule and class name.  This allows us to
handle import errors ourself.