retrieveObjectByPrimaryKey now loks int he backing store (and cache)
first, and doesn't use the index at all in that case.

Added storeObject(Record r, Boolean writeThru) method that would allow
one to recreate the index, or refresh the index for a given oject,
from the backing store as "master"

Added some additional handling of errors/null objects and clearing the
cache, as well as some other error and consistency checks.

Merged the old person test and expense test methods into one test method
to test one index with two record types, each using different storeMode.

Added some more low-level checks to the testFileBackingStore() test.