Be more specific about LSM's requirement for non-zero-length data items,
the generic 'cursor not set' error message is misleading.
Restructure LSM and KVS data-sources; the top-level object is a "file:"
or a "table:", KVS devices are configured on create with "source:XXX",
LSM is configured on create with "type:lsm".
Use a Berkeley DB home directory relative to the WiredTiger home.