Fix EAD export issue with the desc ID, fixes #4269

Squashed commit of the following:

commit 7ee0a621357fae34f3e36702a937e3b42b69035e
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Tue Mar 12 03:11:51 2013 +0100

    Change Xpath query for description identifier

commit b2904fd5243da9a6b01cf73d38e803da0f8d8af4
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Tue Mar 12 02:44:03 2013 +0100

    Improve code

commit b520b5badc75d8b233bfc77eb87a7080db4d7090
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Wed Feb 27 01:33:35 2013 +0100

    Change EAD's description identifier import, fixes #4269

commit 40c4170922f8c57533f7e8a7e58ee383ca0261b3
Author: José Raddaoui Marín <raddaouimarin@gmail.com>
Date:   Tue Feb 26 21:28:46 2013 +0100

    Add identifier attribute to <eadid> in EAD export