Reimplement "replay -a" with minimal debugger-less replay loop.
Inline replay_trace_frames into caller.
Remove unused print_process_state.
Remove unnecessary fflush.
Factor out unusual path where debugger is not launched before end of trace.
Remove stashed_dbg and instead track in a boolean whether we're ready to service gdb requests.
Change some GdbContext* parameters to GdbContext&.

Also removes redundant process-debugger-messages step.