Corrected issue in connection where the same history handler may be
added registered multiple times for a given reference and location pair,
which meant that commitLogFor or rejectLogFor could be invoked more than
just once for the history handlers registered too many times. Now, a
history handler is registered just once; when they start their logging.

Signed-off-by: Jakob Brandsborg Ehmsen <jakobehmsen.github@gmail.com>