Bug 11826: Add unit tests for Koha::XSLT_Handler

Bug 11826: Add unit tests for Koha::XSLT_Handler

Test plan:
Verify if XSLT_Handler.t passes.
You could also sabotage the test by removing one of the test xsl files.
Or you could 'repair' the bad xsl file (test02). Remove the second line
redefining the xsl variable.
In all those cases the unit test should fail now.. Discard your changes :)

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Test pass. No koha-qa errors.

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>