handle trains being deleted and then immediately re-interposed

I don't know why ATS would do this, but like, I guess we have to deal with it now ;w;

(reverse chronological order)

May 28 16:36:51 intertube intertube-scraper[1303870]:   archived X-train-9R20, 80 recs / 76 uniq-trks, last: #<TRACKERNET-TRAIN 9R20 (l=/s=000/t=0/n=?) At Wo>
May 28 16:36:51 intertube intertube-scraper[1303870]:  <INFO> [16:36:51] trackernet trackernet.lisp (archive-trains) -
May 28 16:36:44 intertube intertube-scraper[1303870]:   ...but destination train 9R20 already existed, aborting!
May 28 16:36:44 intertube intertube-scraper[1303870]:  <WARN> [16:36:44] trackernet trackernet.lisp (stomp-td-message-handler) -
May 28 16:36:44 intertube intertube-scraper[1303870]:   interpose in berth 0357 links 9R20 to 9R20, rescuing
May 28 16:36:44 intertube intertube-scraper[1303870]:  <INFO> [16:36:44] trackernet trackernet.lisp (stomp-td-message-handler) -
May 28 16:36:43 intertube intertube-scraper[1303870]:   Deleting train with headcode 9R20
May 28 16:36:43 intertube intertube-scraper[1303870]:  <INFO> [16:36:43] trackernet trackernet.lisp (enqueue-td-deletion) -
May 28 16:36:43 intertube intertube-scraper[1303870]:   in berth 0357, 9R20 cancelled