LP#1078593 Assorted small Serial.pm fixes

LP#1078593 Assorted small Serial.pm fixes

1) fleshed_issuance_alter() changes
  - First, if one of the inner updates returns an event, abort early.
    Otherwise, we might overwrite the event while looping and lose
    the error.
  - Second, add authtoken to the created editor.  This editor gets
    passed around, and other functions might look for it there.

2) pass $type down into _summarize_contents()
  - Right now, we have a bug where supplement/index contents in a
    merged MFHD record will get added to the basic contents (and
    vice-(vice-)versa).  By passing in $type, we can assure that
    we only return the type of contents we are looking for.

3) _prepare_summaries() should acknowledge empty summaries
  - Under normal use, summaries will generally grow, and never shrink
    to nothing.  However, we must still handle cases where we have
    discarded/deleted our last issuance, and in those cases, make sure
    we "empty" the generated_coverage field in our summary.

Signed-off-by: Dan Wells <dbw2@calvin.edu>
Signed-off-by: Kathy Lussier <klussier@masslnc.org>
Signed-off-by: Ben Shum <bshum@biblio.org>