event: ease up subclassing

use `self.__class__` instead of explicit class name
Revert "event: ease up subclassing"

This reverts commit 1234e039556fa1c2ad04f49510e290839a3c84b6.
Doesn't work as intended, see
http://stackoverflow.com/questions/4235078/how-to-avoid-infinite-recursion-with-super.
trace cleanup merge: compare array data not traces, also merging traces
that have some discrepancies in extra stats header like e.g. mseed
because originating from different files