Fix scraper problems with some special chars

1. Remove "ToLower()" from Scraper::FindMovie() as it break UTF-8 and unnecessary
2. Don't use "isalnum" where standard says "US-ASCII"

This should fix http://trac.xbmc.org/ticket/14749 and errors like that: http://forum.xbmc.org/showthread.php?tid=178672 (notice problem with German UI - isalnum(umlaut) is true)