synchronize_time: reset when clock is warped

[c-andy-martin]

If either the hardware clock or system clock warp, reset the EMA to
prevent incorrect clock values from being used. Detect the warp by
putting a limit on the absolute error between the synchronized clock
and the system clock. When a warp is detected, reset the EMA to force
the clocks to resynchronize. Use the system clock until the EMA has
stabalized again.

[tonybaltovski]

@c-andy-martin, I am so sorry, I totally missed this PR. Thanks for this!