A checkpoint (game_save) waits for a safe moment and gives up after
240 ticks; it checks every 10. Those counts were advanced once a frame,
which on the Xbox was once a tick. At 60 frames a second or more a
checkpoint gave up in a few seconds or less, often before the fight it
waited for was over, so few checkpoints came: on Halo (a30) the player
could get only the first. The counts now advance once a game tick, as
the Xbox's did: 8 seconds at any frame rate.
tools/test_checkpoint_timing.py checks it at 30 to 990 frames a second.
(cherry picked from commit abc42998232b6261220a764e6de44641067ff2f5)
Milenko
ce59b93165