PK_ERROR_code_t     PK_MARK_ask_state
(
--- returned arguments ---
PK_MARK_t    *const current,       --- current (or immediately previous) mark
                                   --- (possibly 0)
PK_LOGICAL_t *const is_at_mark     --- whether modeller is at mark
)


This function returns the current state of the non-partitioned PK rollback
system.


Specific Errors:
    PK_ERROR_mark_not_started      non-partitioned PK rollback is not active


This function should only be called when the non-partitioned PK rollback system
has been started via PK_MARK_start.

It returns the current or most recently set mark, and whether the modeller
is at that mark.  If no mark has been set, it will be returned as 0.