PropertyModifier: multibyte-safe upper/lowercase

fixes #710

library/Director/PropertyModifier/PropertyModifierLowercase.php

@@ -8,6 +8,6 @@ class PropertyModifierLowercase extends PropertyModifierHook
 {
     public function transform($value)
     {
-        return strtolower($value);
+        return \mb_strtolower($value, 'UTF-8');
     }
 }

library/Director/PropertyModifier/PropertyModifierUppercase.php

@@ -8,6 +8,6 @@ class PropertyModifierUppercase extends PropertyModifierHook
 {
     public function transform($value)
     {
-        return strtoupper($value);
+        return \mb_strtoupper($value, 'UTF-8');
     }
 }