The fixes for failures caused by strtoupper & strtolower on systems using Turkish locale.

strtoupper & strtolower functions in (as explained here ) PHP are locale aware and refuse to convert the chars that is not alphabetic to its language. Thus on the systems that use locale "tr_TR.UTF-8" strtoupper & strtolower fails because of Turkish 'I'. Since the lowercase of 'I' is 'ı' (w/o dot) and uppercase of 'i' is 'İ', case conversion functions of PHP thinks they are not alphabetic and refuse to convert 'I' to 'i' or 'i' to 'I'. So I changed the relevant lines of code with mbstring ones. mb_ ones successfully make the conversions.

I reported a feature request to PHP team but they are not willing to fix it and it has been there since 2002.
https://bugs.php.net/bug.php?id=67815 (My feature request)
https://bugs.php.net/bug.php?id=18556 (Similar bug reports that goes nowhere)
https://bugs.php.net/bug.php?id=35050

Signed-off-by: Ongun Kanat <ongun.kanat@gmail.com>