Bug 12076: better detect an untranslatable template construct

Per bug 6458, template constructs of the form

<li [% IF (foo) %]selected="selected"[% END %]...

are forbidden as they can cause problems with translated templates.
However, the tt_valid.t test currently doesn't catch the variation
where '-' is used to suppress extra whitespace:

<li [%- IF (foo) -%]selected="selected"[%- END -%]...

This patch corrects the issue.

To test:

[1] Temporarily add the following line to a template file:

<li [%- IF a -%]a="a"[%- END -%] />

[2] Run prove -v xt/tt_valid.t.  Note that no error is reported.
[3] Apply the patch, and rerun the tt_valid.t test.  This time,
    an error should be reported.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>

Works well, detects the forbidden pattern
No koha-qa errors.

Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Works as described, passes all tests and QA script.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>