Refactors getUniqueCachingID() and getCacheFilePath() into private methods and introduces deleteCacheFile() as public method.
ws
Tests for existence of cache file before deleting it.
dbrow3mapper no longer responsible for its own initialization.
improves interface to dbrow3mapper by promoting `applicationName` to argument to init()
improves interface between application and dbrow mapper ..

.. by promoting `useCacheFile` to argument
use actual boolean literal
deletion of cache file is now responsibility of init()
Merge pull request #2 from singlebrook/delete-cache-file-sometimes

Delete cache file sometimes