Bug 22948: Markup error in OPAC bibliographic detail template

This patch addresses one markup problem in opac-detail.tt which triggers
a validation error.

To reproduce the problem, view the normal bibliographic detail page for
a record in the OPAC. Run the page through the W3C validation service:
https://validator.w3.org. Either by pasting in the URL for the search
results (if web accessible) or by viewing source, copying, and pasting
into "Validate by Direct Input."

This patch addresses one specific error:

 - "The aria-labelledby attribute must point to an element in the same
   document."

To test, apply the patch and try again to reproduce the validation
errors. Those errors should no longer be present. There should be no
visible change to the page.

Test the "Save record -> Dublin Core" menu item. It should trigger a
modal window.

Signed-off-by: Maryse Simard <maryse.simard@inlibro.com>
Signed-off-by: Bin Wen <bin.wen@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
(cherry picked from commit a3da6d6825)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

koha-tmpl/opac-tmpl/bootstrap/en/includes/opac-detail-sidebar.inc

@@ -90,7 +90,7 @@
 </ul>
 
 <!-- Dublin Core Modal Form -->
-<div class="modal hide" id="exportModal_" tabindex="-1" role="dialog" aria-labelledby="exportLabelexportModal_" aria-hidden="true">
+<div class="modal hide" id="exportModal_" tabindex="-1" role="dialog" aria-labelledby="exportModalLabel" aria-hidden="true">
     <div class="modal-header">
         <button type="button" class="closebtn" data-dismiss="modal" aria-hidden="true">&times;</button>
         <h3 class="modal-title" id="exportModalLabel">Exporting to Dublin Core...</h3>