We were failing to mark channels as resolved b/c we weren't using later
events to external (but originated from this account) events as signals
to run the channel resolution check.
This fixes that, and adds a test.
Any file in this directory which is executable and whose name only
consists of alphanumeric characters, space, '.', '-' or '_' will be
automatically loaded when lightningd starts (unless suppressed with
commandline options).