assign exits (exit codes).

* in assign_wrapper, no longer return any status from assign to the
  caller. This was pointless. Instead, return 0 on success, 1 on
  controlled error, and -1 on uncontrolled error (die() called
  someplace). Add in CANRECOVER bit whenever the wrapper exits, even
  if uncontrolled, by putting in an END block to catch the die. This
  should prevent certain cases where a swapmod error would be flagged
  as not recoverable.

* Remove most of the assign output processing since we no longer
  return its codes. Still print a portion of it to the log though.

* Change call to fatal() in assign_wrapper; do not pass an exitcode
  since in every case it was the same damn thing!

* Change tbswap to no longer carry assign_wrapper exit code to its
  exit.

* Change the batch daemon to treat all errors as continuable (keep
  batch queued) unless exit code is -1. We will need to revisit this a
  bit perhaps, when Rob adds precheck code.