conf: route service conditions through one owner primitive

A service's condition was computed with mkcond() at each of the six
sites that assert or clear it, and svc_find_by_cond() reimplemented
the reverse lookup a seventh time.  maybe_clear_cond() had its own
scan for another service supplying the same condition.

svc_cond_owner() answers who owns a condition, svc_cond_nth() walks
the conditions a service owns, and svc_cond_set()/svc_cond_clear()
apply to all of them.  svc_find_by_cond() becomes a wrapper, and
maybe_clear_cond() keeps its rule per condition rather than for the
one it used to compute.

The provides[] storage lands here unused, since svc_cond_nth() reads
num_provides.  Nothing sets it yet, so a service still owns exactly
its own pid/<ident> and there is no functional change.

Signed-off-by: Joachim Wiberg <troglobit@gmail.com>

plugins/pidfile.c

@@ -148,12 +148,12 @@ static void pidfile_update_conds(char *dir, char *name, uint32_t mask)
 		}
 
 		if (svc->notify == SVC_NOTIFY_PID)
-			cond_set(cond);
+			svc_cond_set(svc);
 		if (svc->notify == SVC_NOTIFY_PID || svc->notify == SVC_NOTIFY_NONE)
 			service_ready(svc, 1);
 	} else if (mask & IN_DELETE) {
 	sneaky_zebra:
-		cond_clear(cond);
+		svc_cond_clear(svc);
 		if (svc->notify == SVC_NOTIFY_PID)
 			service_ready(svc, 0);
 	}