codebase cleanup: junked unnecessary class property "dbHandle", method getDBHandle() and local variable $DB.
cleanup: removed obsolete static class member $DB_TRANSACTION_RETRY_COUNT and replaced any references to it with Ilios_Database_Constants::TRANSACTION_RETRY_COUNT
codebase cleanup: replaced obsolete variable Audit_Event::$CREATE_EVENT_TYPE with constant Ilios_Model_AuditUtils::CREATE_EVENT_TYPE
codebase cleanup: replaced obsolete variable Audit_Event::$UPDATE_EVENT_TYPE with constant Ilios_Model_AuditUtils::UPDATE_EVENT_TYPE
codebase cleanup: replaced obsolete variable Audit_Event::$DELETE_EVENT_TYPE with constant Ilios_Model_AuditUtils::DELETE_EVENT_TYPE
updated code comments.
Merge pull request #91 from ucsflibtopfstedt/cleanup

codebase cleanup