Have WriteFragmentHeader accept a FragmentPtr parameter to be used as the location for dropping data (if necessary)
SharedMemoryEventManager maintained a list of FragmentPtrs used for providing DataReceiverManager locations to receive Fragment data for Fragments which are to be dropped (due to incomplete events). This would cause problems if multiple receivers tried to drop Fragments simultaneously, and a more elegant solution is for each receiver thread to maintain its own FragmentPtr for this purpose.
Feature implemented in artdaq/feature/PassDroppedDataPointerToSMEM.
Behavior change: SMEM should be able to handle any combination of dropped Fragments from multiple receives without resource contention of the dropped_frags_ member (which no longer exists in this branch).