Fix a problem when translations contain   various XSL files

Fix a problem when translations contain   various XSL files

With new 3.6.1 translation files, the lake of 'nbsp' entity definition make
fail t/00-valid-xml.t test.

This patch applies to HEAD and 3.6.x.

How to test:

  - checkout 3.6.x branch
  - generate French templates:
    cd misc/translator
    ./translate install fr-FR
    cd ../..
  - run test:
    prove -v t/00-valid-xml.t
    you get failing error message
  - apply this patch
  - run test again: it passes

Signed-off-by: Frédéric Demians <f.demians@tamil.fr>
http://bugs.koha-community.org/show_bug.cgi?id=7141