--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.
HRAbsenceType:

 * Save activity_type_id based on OptionValue.value (not OptionValue.id)
 * Add helper for listing all activity-types
HR-224 - Fix initialization of "Absence" and "Public Holiday" activity types

The error test was opposite-right.
Merge pull request #282 from totten/master-absence-model

HR224 - HRAbsence