[i18n] translation.php ingore custom-add string

[David Chang]

Hi all:
Translation.php seems ingore my custom-added string in
turba/config/attritute.php file,when "translation.php update --locale=zh_TW
"executed.

Here is my custom-add string in attritute.php
-----------------------------------
$attributes['uid'] = array(
    'label' => _("Uid"),
    'type' => 'text',
    'required' => false
);
$attributes['unit'] = array(
    'label' => _("Unit"),
    'type' => 'text',
    'required' => false
);
$attributes['url'] = array(
    'label' => _("Url"),
    'type' => 'text',
    'required' => false
);

Here is what i do for translation.php
-------------------------------------
#cd horde/po
#./translation.php update --locale=zh_TW
#cd turba/po
#grep "Unit" zh_TW.po

[return empty result]