Description:
------------
I found mb_stristr has a bug in before_needle's description,When try to translate 
mb_stristr to Chinese.
Actually, if set "before_needle" to FALSE,returned string including 
needle,otherwise excluding needle,but the doc is the reverse.
Here is the patch for this bug.

Test script:
---------------
<?php
$haystack = 'abcdefg';
$needle = 'cd';
echo mb_strstr($haystack,$needle,true),"\n";
echo mb_strstr($haystack,$needle,false),"\n";

echo mb_stristr($haystack,$needle,true),"\n";
echo mb_stristr($haystack,$needle,false),"\n";