1.0.23.60: fix bug 354: XEPs in backtraces, properly this time

1.0.23.60: fix bug 354: XEPs in backtraces, properly this time

 * Don't terminate the block in MAYBE-TERMINATE-BLOCK even if the node
   is a call to a function that never returns if it is also the tail
   end of a XEP -- this allows TCO to deal with the XEP.

 * More stale bugs:
   ** 143 -- cannot replicate, interrupt handling has been robustified
      and partially redesigned since than, so confidence that this is
      really gone is reasonably high.
   ** 238 -- has gotten fixed at some point.