Bug 8665: DOM indexing fails to index some bib records

Bug 8665: DOM indexing fails to index some bib records

Use a user-specified field for z:id.

This patch also fixes an excess space before the index in the MARC21
biblio index definitions, which someone fixed in the generated file
but not in the source file it should have been fixed in.

Signed-off-by: Chris Cormack <chris@bigballofwax.co.nz>
Signed-off-by: Elliott Davis <elliott@bywatersolutions.com>
Conflicts:
	etc/zebradb/marc_defs/marc21/authorities/authority-zebra-indexdefs.xsl

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>