More timer junk, have to match the return value even if unused.
Match return value of start_link.

If it's not {ok, Pid}, we won't be able to trace anyway.
Simplify test in case clause via extraction.

NB @Vagabond: There were several possibilities tested that according
to the code and type signatures could never occur. There is possibly
an unintended outcome here that needs to be addressed.
Whitespace cleanup
Backport fixes from later supervisor versions and match cancel_timer return.
riak_core_pw_auth:hash_password/1 never returns {error, _}.
Remove more legacy gossip cruft.
Fix some types around coverage requests.

* Coverage requests to multiple vnodes reconstruct the original
  sender() to include the {partition(), node()} in the "reference".
  Widened the type to include that case.
* Added an actual type for keyspace specifications.