Bug 8852: DOM XSL now handles subfield substring extraction

Bug 8852: DOM XSL now handles subfield substring extraction

This patch modify koha-indexdefs-to-zebra.xsl in order to add the
ability to populate indexes with subfield substring.

It's now possible to understand such construction as:

<index_subfields xmlns="http://..." tag="100" subfields="a" offset="7" length="1">
  <target_index>tpubdate:s</target_index>
</index_subfields>

Signed-off-by:Mathieu Saby <mathieu.saby@univ-rennes2.fr>

I applied the patch and ran
  xsltproc koha-indexdefs-to-zebra.xsl ../marc_defs/unimarc/biblios/biblio-koha-indexdefs.xml \
     > ../marc_defs/unimarc/biblios/biblio-zebra-indexdefs.xsl
I looked at the generated file. It looks nice.
Then I copied it file in my INSTALLDIR/etc/zebra.... and reindexed my
records with rebuild_zebra.pl
I made some searches on coded position index and non coded position
indexes, everything works.

http://bugs.koha-community.org/show_bug.cgi?id=8252

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>