Clean up event log merge code

Clean up event log merge code

Fix a decade-old ridiculous qsort function bug. Managed to subtract
floating-point numbers as if they were integers, leading to
manufactured time-paradoxes. That completely confuses g2, leading to
the summary disappearance of entire tracks' worth of data at high zoom
levels.

Add a manual alignment tweak parameter to elog_merge, users can
dial-out time paradoxes caused by NTP-grade clock synchronization.
The event-logger has a precision of O(100ns), whereas NTP
synchronization is O(1ms).

Change-Id: I69dedabaa314f69f9df74ec9ee66e21e6c87f703
Signed-off-by: Dave Barach <dave@barachs.net>