action: synchronize_with - return status for out-of-order synchronization

action: synchronize_with - return status for out-of-order synchronization

"synchronize_with()" now can return a boolean status, rather than just
using an ASSERT(). This allows synchronize_with() to be called with
actions that are against the program trace order, then return a status
to signify success/failure. This will allow, for instance, release
sequence calculations to simply abort this single execution, not the
whole model-checker.