Bug 7419: correct LCCN/see from indexing

This patch adds indexes for previous headings and LCCN for MARC21
authority records. See the following patch for a test plan to confirm
that the indexing works correctly.
Bug 7419: General-purpose record deduplicator

This patch adds a script for deduplicating records. It is most useful
for authority records but by design could be easily extended for use
with bibliographic records, if someone had a good use case.

To test using the sample records attached to the bug (MARC21 only):
1) Apply patches.
2) Import the sample records (sampleauths.mrc) file into Koha and
   make sure that they get indexed (by waiting until rebuild_zebra.pl
   runs automatically or by running rebuild_zebra.pl -a -z [-x] manually)
3) Deduplicate based on LCCN (replace {FIRSTAUTH} with the authid of the
   first imported record; on my system that number is 367123668; this is
   not actually necessary, but if you have a lot of authority records,
   the process could take quite a while otherwise):

   > misc/migration_tools/dedup_records.pl -t -v -a \
     -l "authid >= {FIRSTAUTH}" -r -m "lc-card/010a" -s date

4) Check that you have 21 duplicate records replaced from amongst the
   new records (you will quite possibly have more than 21 duplicate
   records reported, depending on whether you have any of these
   authorities already, but you should have at least the 21).
5) Deduplicate based on genre heading, preferring Library of Congress
   authorities to local authorities:

   > misc/migration_tools/dedup_records.pl -t -v -a \
     -l "authid >= {FIRSTAUTH}" -r -m "he/155a" -s "source=DLC" -s date

6) Check that you have 3 duplicate records replaced from amongst the new
   records.
7) Sign off.

Complete POD documentation:

SYNOPSIS
         dedup_records.pl --match=1 -a

         dedup_records.pl --match="LC-card-number/010a" --select="date" \
           --limit="authid > 367123592" -a

         dedup_records.pl --match="Match/100abcdefghijklmnopqrstuvwxyz" \
           --select="source=DLC" --select="date" \
           --limit="authtypecode='PERSO_NAME'" -a

DESCRIPTION
       This script will identify duplicate records, and either suggest
       that you merge them (in the case of bibliographic records) or
       automatically merge them for you (in the case of authority records).

OPTIONS
       --help  Prints this help

       -v|--verbose
               Print verbose log information (warning: very verbose!).

       -t|--test
               Do not actually make any changes to the database, just
               report what changes would be made.

       -r|--report
               Print a report of what happened during the run.

       -l|--limit=S
               Only process those records that match the user-specified
               WHERE clause (the WHERE is implied and should not be
               included on the command line).

       -a|--authorities
               Check for duplicate authorities rather that duplicate
               bibliographic records.

       -s|--select=s
               Repeatable. Specify how to identify which record to
               prefer. See the section on SELECTORS below.

       -m|--match=s
               Specifies the matching rule to use. This can be the
               numeric ID of a matching rule that you have already
               configured (preferred), or you can specify a matching
               rule on the command-line in the following format:

                   <index1>/<tag1><subfield1>[##<index2>/<tag2><subfield2>[##...]]

               Examples:

                   at/152b##he-main/2..a##he/2..bxyzt##ident/009@
                   authtype/152b##he-main,ext/2..a##he,ext/2..bxyz
                   sn,ne,st-numeric/001##authtype/152b##he-main,ext/2..a##he,ext/2..bxyz

       -c|--check=s
               Only relevant when you are using a matching rule
               specified on the command line. Specifies sanity checks to
               use to ensure that the records are really duplicate. The
               format is <tag1><subfields1>[,<tag2><subfields2>[,...]]

               Examples:

                   200abxyz will check subfields a,b,x,y,z of 200 fields
                   009@,152b will check 009 data and 152$b subfields

SELECTORS
       This script supports a number of selectors for choosing which
       record is "better."

       score   Prefer the record which is the best match based on the
               specified matching rule. This will probably only be
               useful in cases where the matching rule will not match
               the source record, since the source record will
               automatically be given a score of 2 * the matching rule
               threshold if it wasn't picked up by the matcher.

       date    Prefer the record which is newer based on the 005 field.

       source=ABC
               MARC21 only. Prefer records which come from ABC based on
               the 003 field.

       usage   Authorities only. Prefer the record used in the most
               bibliographic records.

       ppn     UNIMARC only. Prefer records which have a PPN in the 009
               field.
Correct schema.org context for item status

We were inserting the <link> element inside an open <td> element, which
HTML parsers, even the most forgiving, do not like very much.

Signed-off-by: Dan Scott <dan@coffeecode.net>