Revert "Don't need Horde_String::lower() here - we are only matching ASCII text so if this are indeed some crazy multiibyte string, it wouldn't match anyway"

This reverts commit d55fcad8e73062d201a6e4083032c3a84c006fad.

*Those* Horde_String methods are not for dealing with multibyte strings, but
 for working around PHP bugs when using certain locales.