properly test `killaddon` (fix #28)

Tests both
* assassinate (which coverreport can see)
* self-destruct (which coverage can't see)

Adds:
* `make fixtures` phony target.
  - note this has to run before cover, or files might not get copied

(unrelated to #27, despite similar symptoms)

self-destruct, wip

self-destructing addon code

more wip