--HR-224 HRAbsence modifications
HRAbsenceType - Restore code which creates two activity types. Autoformat.
HRAbsenceType - Fix label of credit type. Fix defaults for allow_credits/allow_debits.
api/v3/HRAbsence* - Remove references to is_primary (looks like copy/pasted dead code)
HRAbsenceType - Remove unnecessary error check. The call to civicrm_api3() will throw exceptions.
HRAbsenceType - Fixes:

 * Don't set default *_activity_type_id to 1
 * When updating, don't change *_activity_type_id just because label has changed
HRAbsence - Remove references to non-existent entity, "HRAbsence"

Per http://issues.civicrm.org/jira/browse/HR-224 , we use activity
records for the actual absences.