Feature 1451 : localization with gettext

Use php-gettext (developpement version rev43, because of php5.3) as fallback
Use native language (english) instead of key for translation
Keep directory en_UK for english customization
Need some refactoring for plurals

Todo : managing plugins in the same way

git-svn-id: http://piwigo.org/svn/trunk@5021 68402e56-0260-453c-a942-63ccdbb3a9ee

include/calendar_base.class.php

@@ -95,7 +95,7 @@ class CalendarBase
     }
     elseif ('any' === $date_component )
     {
-      $label = l10n('calendar_any');
+      $label = l10n('All');
     }
     return $label;
   }
@@ -192,7 +192,7 @@ class CalendarBase
         array( 'start' )
           );
       $nav_bar_datas[]=array(
-        'LABEL' => l10n('calendar_any'),
+        'LABEL' => l10n('All'),
         'URL' => $url
       );
     }