[Gecode] Flushing propagator resources

[Christian Schulte]

Dear all,

sometimes it can be necessary to flush resources used by propagators (such
as memory used for data structures achieving incremental propagation). A
typical secanrio is to store a space for backtracking after propagation has
been performed on it (happens now and then but not in depth-first search).

To achieve this, a propagator can implement a virtual void flush(void)
member function and spaces also have the corresponding function: the
function is invoked on all propagators registered for explicit deletion (as
these are the propagators using explicit resources).

In case you use propagators with resources please also implement an
appropriate flush member function.

Cheers
Christian

--
Christian Schulte, http://www.imit.kth.se/~schulte/