Fix issue #16953886: History and batterystats checkin summary...

...start timestamps are in 1970s

Look for the wall clock time being very small, and try to update
it to a better value if we see one.

Also handle time change events to update the current time we a re
tracking.

Change-Id: Ifbae2b8c43ab5baa75ee4f672a752a542e23b52d